diff --git a/phpunit/class-wp-theme-json-test.php b/phpunit/class-wp-theme-json-test.php
index 36b8218785f216..8d2f470efe60fe 100644
--- a/phpunit/class-wp-theme-json-test.php
+++ b/phpunit/class-wp-theme-json-test.php
@@ -46,6 +46,52 @@ public static function set_up_before_class() {
 		static::$user_id = self::factory()->user->create();
 	}
 
+	/**
+	 * Pretty print CSS in test assertions so that it provides a better diff when a test fails.
+	 * Without this: the failing test outputs the entire css string as being different.
+	 * With this: the failing test only highlights the specific CSS rule that is different.
+	 *
+	 * @param string $css A string of raw css with no line breaks.
+	 * @return string The css with line breaks.
+	 */
+	private static function pretty_print_css( $css ) {
+		$css = str_replace( '{', " {\n", $css );
+		$css = str_replace( '}', "}\n\n", $css );
+		$css = str_replace( ';', ";\n", $css );
+		return $css;
+	}
+
+	/**
+	 * Asserts that two CSS strings are equivalent, but outputs
+	 * pretty printed test failures along with the raw css.
+	 *
+	 * - The pretty printed assertions are useful for understanding what actually changed.
+	 * - The raw css is included as it's useful for updating the test case's expected CSS.
+	 *
+	 * Inspired by:
+	 * https://stackoverflow.com/questions/6832263/phpunit-assertion-failed-but-i-want-to-continue-testing
+	 *
+	 * @param string $expected The expected CSS.
+	 * @param string $actual   The actual CSS.
+	 */
+	private function assertSameCSS( $expected, $actual, $message = '' ) {
+		$pretty_expected = self::pretty_print_css( $expected );
+		$pretty_actual   = self::pretty_print_css( $actual );
+
+		try {
+			$this->assertSame( $pretty_expected, $pretty_actual, $message );
+		} catch ( PHPUnit_Framework_ExpectationFailedException $e ) {
+			// Test failures are thrown as exceptions by PHPUnit.
+			// Catch the exception and re-throw it, but with the
+			// raw css appended.
+			$raw_actual_output =
+				"\n\nIf the change is expected, update the test case to this CSS:\n$actual";
+			throw new PHPUnit_Framework_ExpectationFailedException(
+				"$e$raw_actual_output"
+			);
+		}
+	}
+
 	public function test_get_settings() {
 		$theme_json = new WP_Theme_JSON_Gutenberg(
 			array(
@@ -556,10 +602,10 @@ public function test_get_stylesheet() {
 		$presets   = '.has-grey-color{color: var(--wp--preset--color--grey) !important;}.has-grey-background-color{background-color: var(--wp--preset--color--grey) !important;}.has-grey-border-color{border-color: var(--wp--preset--color--grey) !important;}.has-custom-gradient-gradient-background{background: var(--wp--preset--gradient--custom-gradient) !important;}.has-small-font-size{font-size: var(--wp--preset--font-size--small) !important;}.has-big-font-size{font-size: var(--wp--preset--font-size--big) !important;}.has-arial-font-family{font-family: var(--wp--preset--font-family--arial) !important;}';
 		$all       = $variables . $styles . $presets;
 
-		$this->assertSame( $variables, $theme_json->get_stylesheet( array( 'variables' ) ) );
-		$this->assertSame( $styles, $theme_json->get_stylesheet( array( 'styles' ) ) );
-		$this->assertSame( $presets, $theme_json->get_stylesheet( array( 'presets' ) ) );
-		$this->assertSame( $all, $theme_json->get_stylesheet() );
+		$this->assertSameCSS( $variables, $theme_json->get_stylesheet( array( 'variables' ) ) );
+		$this->assertSameCSS( $styles, $theme_json->get_stylesheet( array( 'styles' ) ) );
+		$this->assertSameCSS( $presets, $theme_json->get_stylesheet( array( 'presets' ) ) );
+		$this->assertSameCSS( $all, $theme_json->get_stylesheet() );
 	}
 
 	public function test_get_styles_for_block_support_for_shorthand_and_longhand_values() {
@@ -618,8 +664,8 @@ public function test_get_styles_for_block_support_for_shorthand_and_longhand_val
 
 		$group_styles = ':root :where(.wp-block-group){border-radius: 10px;margin: 1em;padding: 24px;}';
 		$image_styles = ':root :where(.wp-block-image){margin-bottom: 30px;padding-top: 15px;}:root :where(.wp-block-image img, .wp-block-image .wp-block-image__crop-area, .wp-block-image .components-placeholder){border-top-left-radius: 10px;border-bottom-right-radius: 1em;}';
-		$this->assertSame( $group_styles, $theme_json->get_styles_for_block( $group_node ) );
-		$this->assertSame( $image_styles, $theme_json->get_styles_for_block( $image_node ) );
+		$this->assertSameCSS( $group_styles, $theme_json->get_styles_for_block( $group_node ) );
+		$this->assertSameCSS( $image_styles, $theme_json->get_styles_for_block( $image_node ) );
 	}
 
 	public function test_get_stylesheet_skips_disabled_protected_properties() {
@@ -647,8 +693,8 @@ public function test_get_stylesheet_skips_disabled_protected_properties() {
 		);
 
 		$expected = static::$base_styles . ':where(.wp-block-columns.is-layout-flex){gap: 2em;}:where(.wp-block-columns.is-layout-grid){gap: 2em;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet() );
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet() );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ) ) );
 	}
 
 	public function test_get_stylesheet_renders_enabled_protected_properties() {
@@ -669,8 +715,8 @@ public function test_get_stylesheet_renders_enabled_protected_properties() {
 		);
 
 		$expected = ':where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.wp-site-blocks) > * { margin-block-start: 1em; margin-block-end: 0; }:where(.wp-site-blocks) > :first-child { margin-block-start: 0; }:where(.wp-site-blocks) > :last-child { margin-block-end: 0; }:root { --wp--style--block-gap: 1em; }.is-layout-flow  > :first-child{margin-block-start: 0;}.is-layout-flow  > :last-child{margin-block-end: 0;}.is-layout-flow  > *{margin-block-start: 1em;margin-block-end: 0;}.is-layout-constrained  > :first-child{margin-block-start: 0;}.is-layout-constrained  > :last-child{margin-block-end: 0;}.is-layout-constrained  > *{margin-block-start: 1em;margin-block-end: 0;}.is-layout-flex {gap: 1em;}.is-layout-grid {gap: 1em;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){margin-left: auto !important;margin-right: auto !important;}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet() );
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet() );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ) ) );
 	}
 
 	public function test_get_stylesheet_preset_classes_work_with_compounded_selectors() {
@@ -694,7 +740,7 @@ public function test_get_stylesheet_preset_classes_work_with_compounded_selector
 			)
 		);
 
-		$this->assertSame(
+		$this->assertSameCSS(
 			'.wp-block-heading.has-white-color{color: var(--wp--preset--color--white) !important;}.wp-block-heading.has-white-background-color{background-color: var(--wp--preset--color--white) !important;}.wp-block-heading.has-white-border-color{border-color: var(--wp--preset--color--white) !important;}',
 			$theme_json->get_stylesheet( array( 'presets' ) )
 		);
@@ -736,10 +782,10 @@ public function test_get_stylesheet_preset_rules_come_after_block_rules() {
 
 		$all = $variables . $styles . $presets;
 
-		$this->assertSame( $all, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
-		$this->assertSame( $styles, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
-		$this->assertSame( $presets, $theme_json->get_stylesheet( array( 'presets' ) ) );
-		$this->assertSame( $variables, $theme_json->get_stylesheet( array( 'variables' ) ) );
+		$this->assertSameCSS( $all, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $styles, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $presets, $theme_json->get_stylesheet( array( 'presets' ) ) );
+		$this->assertSameCSS( $variables, $theme_json->get_stylesheet( array( 'variables' ) ) );
 	}
 
 	public function test_get_stylesheet_generates_proper_classes_and_css_vars_from_slugs() {
@@ -774,11 +820,11 @@ public function test_get_stylesheet_generates_proper_classes_and_css_vars_from_s
 			)
 		);
 
-		$this->assertSame(
+		$this->assertSameCSS(
 			'.has-grey-color{color: var(--wp--preset--color--grey) !important;}.has-dark-grey-color{color: var(--wp--preset--color--dark-grey) !important;}.has-light-grey-color{color: var(--wp--preset--color--light-grey) !important;}.has-white-2-black-color{color: var(--wp--preset--color--white-2-black) !important;}.has-grey-background-color{background-color: var(--wp--preset--color--grey) !important;}.has-dark-grey-background-color{background-color: var(--wp--preset--color--dark-grey) !important;}.has-light-grey-background-color{background-color: var(--wp--preset--color--light-grey) !important;}.has-white-2-black-background-color{background-color: var(--wp--preset--color--white-2-black) !important;}.has-grey-border-color{border-color: var(--wp--preset--color--grey) !important;}.has-dark-grey-border-color{border-color: var(--wp--preset--color--dark-grey) !important;}.has-light-grey-border-color{border-color: var(--wp--preset--color--light-grey) !important;}.has-white-2-black-border-color{border-color: var(--wp--preset--color--white-2-black) !important;}',
 			$theme_json->get_stylesheet( array( 'presets' ) )
 		);
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root{--wp--preset--color--grey: grey;--wp--preset--color--dark-grey: grey;--wp--preset--color--light-grey: grey;--wp--preset--color--white-2-black: grey;--wp--custom--white-2-black: value;}',
 			$theme_json->get_stylesheet( array( 'variables' ) )
 		);
@@ -834,9 +880,9 @@ public function test_get_styles_for_block_handles_whitelisted_element_pseudo_sel
 		$hover_style = ':root :where(a:where(:not(.wp-element-button)):hover){background-color: green;color: red;font-size: 10em;text-transform: uppercase;}';
 		$focus_style = ':root :where(a:where(:not(.wp-element-button)):focus){background-color: black;color: yellow;}';
 
-		$this->assertSame( $link_style, $theme_json->get_styles_for_block( $link_node ) );
-		$this->assertSame( $hover_style, $theme_json->get_styles_for_block( $hover_node ) );
-		$this->assertSame( $focus_style, $theme_json->get_styles_for_block( $focus_node ) );
+		$this->assertSameCSS( $link_style, $theme_json->get_styles_for_block( $link_node ) );
+		$this->assertSameCSS( $hover_style, $theme_json->get_styles_for_block( $hover_node ) );
+		$this->assertSameCSS( $focus_style, $theme_json->get_styles_for_block( $focus_node ) );
 	}
 
 	/**
@@ -872,8 +918,7 @@ public function test_get_stylesheet_handles_only_pseudo_selector_rules_for_given
 		);
 
 		$expected = ':root :where(a:where(:not(.wp-element-button)):hover){background-color: green;color: red;font-size: 10em;text-transform: uppercase;}:root :where(a:where(:not(.wp-element-button)):focus){background-color: black;color: yellow;}';
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_stylesheet_ignores_pseudo_selectors_on_non_whitelisted_elements() {
@@ -906,8 +951,7 @@ public function test_get_stylesheet_ignores_pseudo_selectors_on_non_whitelisted_
 		);
 
 		$expected = 'h4{background-color: red;color: green;}';
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_stylesheet_ignores_non_whitelisted_pseudo_selectors() {
@@ -940,8 +984,7 @@ public function test_get_stylesheet_ignores_non_whitelisted_pseudo_selectors() {
 		);
 
 		$expected = 'a:where(:not(.wp-element-button)){background-color: red;color: green;}:root :where(a:where(:not(.wp-element-button)):hover){background-color: green;color: red;}';
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 		$this->assertStringNotContainsString( 'a:levitate{', $theme_json->get_stylesheet( array( 'styles' ) ) );
 	}
 
@@ -987,8 +1030,7 @@ public function test_get_stylesheet_handles_priority_of_elements_vs_block_elemen
 		);
 
 		$expected = ':root :where(.wp-block-group a:where(:not(.wp-element-button))){background-color: red;color: green;}:root :where(.wp-block-group a:where(:not(.wp-element-button)):hover){background-color: green;color: red;font-size: 10em;text-transform: uppercase;}:root :where(.wp-block-group a:where(:not(.wp-element-button)):focus){background-color: black;color: yellow;}';
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	/**
@@ -1032,8 +1074,7 @@ public function test_get_stylesheet_with_deprecated_feature_level_selectors() {
 		$block_styles  = ':root :where(.wp-block-calendar){font-size: 3em;}:root :where(.wp-block-calendar table, .wp-block-calendar th){color: green;}';
 		$preset_styles = '.has-green-color{color: var(--wp--preset--color--green) !important;}.has-green-background-color{background-color: var(--wp--preset--color--green) !important;}.has-green-border-color{border-color: var(--wp--preset--color--green) !important;}';
 		$expected      = $base_styles . $block_styles . $preset_styles;
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 
@@ -1063,8 +1104,7 @@ public function test_get_stylesheet_with_block_json_selectors() {
 		);
 
 		$expected = ':root :where(.wp-block-image img, .wp-block-image .wp-block-image__crop-area, .wp-block-image .components-placeholder){border-radius: 374px;}';
-
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_stylesheet_generates_layout_styles() {
@@ -1090,7 +1130,7 @@ public function test_get_stylesheet_generates_layout_styles() {
 		);
 
 		// Results also include root site blocks styles.
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root { --wp--style--global--content-size: 640px;--wp--style--global--wide-size: 1200px; }:where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.wp-site-blocks) > * { margin-block-start: 1em; margin-block-end: 0; }:where(.wp-site-blocks) > :first-child { margin-block-start: 0; }:where(.wp-site-blocks) > :last-child { margin-block-end: 0; }:root { --wp--style--block-gap: 1em; }.is-layout-flow  > :first-child{margin-block-start: 0;}.is-layout-flow  > :last-child{margin-block-end: 0;}.is-layout-flow  > *{margin-block-start: 1em;margin-block-end: 0;}.is-layout-constrained  > :first-child{margin-block-start: 0;}.is-layout-constrained  > :last-child{margin-block-end: 0;}.is-layout-constrained  > *{margin-block-start: 1em;margin-block-end: 0;}.is-layout-flex {gap: 1em;}.is-layout-grid {gap: 1em;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width: var(--wp--style--global--content-size);margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignwide{max-width: var(--wp--style--global--wide-size);}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}',
 			$theme_json->get_stylesheet( array( 'styles' ) )
 		);
@@ -1119,7 +1159,7 @@ public function test_get_stylesheet_generates_layout_styles_with_spacing_presets
 		);
 
 		// Results also include root site blocks styles.
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root { --wp--style--global--content-size: 640px;--wp--style--global--wide-size: 1200px; }:where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.wp-site-blocks) > * { margin-block-start: var(--wp--preset--spacing--60); margin-block-end: 0; }:where(.wp-site-blocks) > :first-child { margin-block-start: 0; }:where(.wp-site-blocks) > :last-child { margin-block-end: 0; }:root { --wp--style--block-gap: var(--wp--preset--spacing--60); }.is-layout-flow  > :first-child{margin-block-start: 0;}.is-layout-flow  > :last-child{margin-block-end: 0;}.is-layout-flow  > *{margin-block-start: var(--wp--preset--spacing--60);margin-block-end: 0;}.is-layout-constrained  > :first-child{margin-block-start: 0;}.is-layout-constrained  > :last-child{margin-block-end: 0;}.is-layout-constrained  > *{margin-block-start: var(--wp--preset--spacing--60);margin-block-end: 0;}.is-layout-flex {gap: var(--wp--preset--spacing--60);}.is-layout-grid {gap: var(--wp--preset--spacing--60);}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width: var(--wp--style--global--content-size);margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignwide{max-width: var(--wp--style--global--wide-size);}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}',
 			$theme_json->get_stylesheet( array( 'styles' ) )
 		);
@@ -1149,7 +1189,7 @@ public function test_get_stylesheet_generates_fallback_gap_layout_styles() {
 		$stylesheet = $theme_json->get_stylesheet( array( 'styles' ) );
 
 		// Results also include root site blocks styles.
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root { --wp--style--global--content-size: 640px;--wp--style--global--wide-size: 1200px; }:where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.is-layout-flex){gap: 0.5em;}:where(.is-layout-grid){gap: 0.5em;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width: var(--wp--style--global--content-size);margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignwide{max-width: var(--wp--style--global--wide-size);}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}',
 			$stylesheet
 		);
@@ -1170,7 +1210,7 @@ public function test_get_stylesheet_generates_base_fallback_gap_layout_styles()
 		$stylesheet = $theme_json->get_stylesheet( array( 'base-layout-styles' ) );
 
 		// Note the `base-layout-styles` includes a fallback gap for the Columns block for backwards compatibility.
-		$this->assertSame(
+		$this->assertSameCSS(
 			':where(.is-layout-flex){gap: 0.5em;}:where(.is-layout-grid){gap: 0.5em;}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}:where(.wp-block-columns.is-layout-flex){gap: 2em;}:where(.wp-block-columns.is-layout-grid){gap: 2em;}:where(.wp-block-post-template.is-layout-flex){gap: 1.25em;}:where(.wp-block-post-template.is-layout-grid){gap: 1.25em;}',
 			$stylesheet
 		);
@@ -1193,7 +1233,7 @@ public function test_get_stylesheet_skips_layout_styles() {
 		remove_theme_support( 'disable-layout-styles' );
 
 		// All Layout styles should be skipped.
-		$this->assertSame(
+		$this->assertSameCSS(
 			'',
 			$stylesheet
 		);
@@ -1243,7 +1283,7 @@ public function test_get_stylesheet_generates_valid_block_gap_values_and_skips_n
 			'default'
 		);
 
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root { --wp--style--global--content-size: 640px;--wp--style--global--wide-size: 1200px; }:where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.wp-site-blocks) > * { margin-block-start: 1rem; margin-block-end: 0; }:where(.wp-site-blocks) > :first-child { margin-block-start: 0; }:where(.wp-site-blocks) > :last-child { margin-block-end: 0; }:root { --wp--style--block-gap: 1rem; }.is-layout-flow  > :first-child{margin-block-start: 0;}.is-layout-flow  > :last-child{margin-block-end: 0;}.is-layout-flow  > *{margin-block-start: 1rem;margin-block-end: 0;}.is-layout-constrained  > :first-child{margin-block-start: 0;}.is-layout-constrained  > :last-child{margin-block-end: 0;}.is-layout-constrained  > *{margin-block-start: 1rem;margin-block-end: 0;}.is-layout-flex {gap: 1rem;}.is-layout-grid {gap: 1rem;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width: var(--wp--style--global--content-size);margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignwide{max-width: var(--wp--style--global--wide-size);}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}' .
 			':root :where(.wp-block-post-content){color: gray;}.wp-block-social-links-is-layout-flow  > :first-child{margin-block-start: 0;}.wp-block-social-links-is-layout-flow  > :last-child{margin-block-end: 0;}.wp-block-social-links-is-layout-flow  > *{margin-block-start: 0;margin-block-end: 0;}.wp-block-social-links-is-layout-constrained  > :first-child{margin-block-start: 0;}.wp-block-social-links-is-layout-constrained  > :last-child{margin-block-end: 0;}.wp-block-social-links-is-layout-constrained  > *{margin-block-start: 0;margin-block-end: 0;}.wp-block-social-links-is-layout-flex {gap: 0;}.wp-block-social-links-is-layout-grid {gap: 0;}.wp-block-buttons-is-layout-flow  > :first-child{margin-block-start: 0;}.wp-block-buttons-is-layout-flow  > :last-child{margin-block-end: 0;}.wp-block-buttons-is-layout-flow  > *{margin-block-start: 0;margin-block-end: 0;}.wp-block-buttons-is-layout-constrained  > :first-child{margin-block-start: 0;}.wp-block-buttons-is-layout-constrained  > :last-child{margin-block-end: 0;}.wp-block-buttons-is-layout-constrained  > *{margin-block-start: 0;margin-block-end: 0;}.wp-block-buttons-is-layout-flex {gap: 0;}.wp-block-buttons-is-layout-grid {gap: 0;}',
 			$theme_json->get_stylesheet()
@@ -1279,7 +1319,7 @@ public function test_get_stylesheet_returns_outline_styles() {
 
 		$expected = ':root :where(.wp-element-button, .wp-block-button__link){outline-color: red;outline-offset: 3px;outline-style: dashed;outline-width: 3px;}:root :where(.wp-element-button:hover, .wp-block-button__link:hover){outline-color: blue;outline-offset: 3px;outline-style: solid;outline-width: 3px;}';
 
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_stylesheet_custom_root_selector() {
@@ -1302,7 +1342,7 @@ public function test_get_stylesheet_custom_root_selector() {
 		);
 		$actual  = $theme_json->get_stylesheet( array( 'styles' ), null, $options );
 
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root :where(.custom){color: teal;}',
 			$actual
 		);
@@ -1360,7 +1400,7 @@ public function test_get_stylesheet_generates_fluid_typography_values() {
 
 		unregister_block_type( 'test/clamp-me' );
 
-		$this->assertSame(
+		$this->assertSameCSS(
 			':root{--wp--preset--font-size--pickles: clamp(14px, 0.875rem + ((1vw - 3.2px) * 0.156), 16px);--wp--preset--font-size--toast: clamp(14.642px, 0.915rem + ((1vw - 3.2px) * 0.575), 22px);}body{font-size: clamp(0.875em, 0.875rem + ((1vw - 0.2em) * 0.156), 1em);}h1{font-size: clamp(50.171px, 3.136rem + ((1vw - 3.2px) * 3.893), 100px);}:root :where(.wp-block-test-clamp-me){font-size: clamp(27.894px, 1.743rem + ((1vw - 3.2px) * 1.571), 48px);}.has-pickles-font-size{font-size: var(--wp--preset--font-size--pickles) !important;}.has-toast-font-size{font-size: var(--wp--preset--font-size--toast) !important;}',
 			$theme_json->get_stylesheet( array( 'styles', 'variables', 'presets' ), null, array( 'skip_root_layout_styles' => true ) )
 		);
@@ -3419,7 +3459,7 @@ public function test_get_property_value_valid() {
 		);
 
 		$expected = 'body{background-color: #ffffff;color: #000000;}:root :where(.wp-element-button, .wp-block-button__link){background-color: #000000;color: #ffffff;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	/**
@@ -3496,7 +3536,7 @@ public function test_get_property_value_loop() {
 		);
 
 		$expected = 'body{background-color: #ffffff;}:root :where(.wp-element-button, .wp-block-button__link){color: #ffffff;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	/**
@@ -3528,7 +3568,7 @@ public function test_get_property_value_recursion() {
 		);
 
 		$expected = 'body{background-color: #ffffff;color: #ffffff;}:root :where(.wp-element-button, .wp-block-button__link){color: #ffffff;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	/**
@@ -3551,7 +3591,7 @@ public function test_get_property_value_self() {
 		);
 
 		$expected = 'body{background-color: #ffffff;}';
-		$this->assertSame( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected, $theme_json->get_stylesheet( array( 'styles' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_styles_for_block_with_padding_aware_alignments() {
@@ -3582,7 +3622,7 @@ public function test_get_styles_for_block_with_padding_aware_alignments() {
 		$expected    = ':where(body) { margin: 0; }.wp-site-blocks { padding-top: var(--wp--style--root--padding-top); padding-bottom: var(--wp--style--root--padding-bottom); }.has-global-padding { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }.has-global-padding > .alignfull { margin-right: calc(var(--wp--style--root--padding-right) * -1); margin-left: calc(var(--wp--style--root--padding-left) * -1); }.has-global-padding :where(:not(.alignfull.is-layout-flow) > .has-global-padding:not(.wp-block-block, .alignfull)) { padding-right: 0; padding-left: 0; }.has-global-padding :where(:not(.alignfull.is-layout-flow) > .has-global-padding:not(.wp-block-block, .alignfull)) > .alignfull { margin-left: 0; margin-right: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.is-layout-flex){gap: 0.5em;}:where(.is-layout-grid){gap: 0.5em;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){margin-left: auto !important;margin-right: auto !important;}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}body{--wp--style--root--padding-top: 10px;--wp--style--root--padding-right: 12px;--wp--style--root--padding-bottom: 10px;--wp--style--root--padding-left: 12px;}';
 		$root_rules  = $theme_json->get_root_layout_rules( WP_Theme_JSON_Gutenberg::ROOT_BLOCK_SELECTOR, $metadata );
 		$style_rules = $theme_json->get_styles_for_block( $metadata );
-		$this->assertSame( $expected, $root_rules . $style_rules );
+		$this->assertSameCSS( $expected, $root_rules . $style_rules );
 	}
 
 	public function test_get_styles_for_block_without_padding_aware_alignments() {
@@ -3610,7 +3650,7 @@ public function test_get_styles_for_block_without_padding_aware_alignments() {
 		$expected    = static::$base_styles . 'body{padding-top: 10px;padding-right: 12px;padding-bottom: 10px;padding-left: 12px;}';
 		$root_rules  = $theme_json->get_root_layout_rules( WP_Theme_JSON_Gutenberg::ROOT_BLOCK_SELECTOR, $metadata );
 		$style_rules = $theme_json->get_styles_for_block( $metadata );
-		$this->assertSame( $expected, $root_rules . $style_rules );
+		$this->assertSameCSS( $expected, $root_rules . $style_rules );
 	}
 
 	public function test_get_styles_with_content_width() {
@@ -3632,7 +3672,7 @@ public function test_get_styles_with_content_width() {
 		);
 
 		$expected = ':root { --wp--style--global--content-size: 800px;--wp--style--global--wide-size: 1000px; }:where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.is-layout-flex){gap: 0.5em;}:where(.is-layout-grid){gap: 0.5em;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width: var(--wp--style--global--content-size);margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignwide{max-width: var(--wp--style--global--wide-size);}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}';
-		$this->assertSame( $expected, $theme_json->get_root_layout_rules( WP_Theme_JSON::ROOT_BLOCK_SELECTOR, $metadata ) );
+		$this->assertSameCSS( $expected, $theme_json->get_root_layout_rules( WP_Theme_JSON::ROOT_BLOCK_SELECTOR, $metadata ) );
 	}
 
 	public function test_get_styles_with_appearance_tools() {
@@ -3651,7 +3691,7 @@ public function test_get_styles_with_appearance_tools() {
 		);
 
 		$expected = ':where(body) { margin: 0; }.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }.wp-site-blocks > .alignright { float: right; margin-left: 2em; }.wp-site-blocks > .aligncenter { justify-content: center; margin-left: auto; margin-right: auto; }:where(.wp-site-blocks) > * { margin-block-start: ; margin-block-end: 0; }:where(.wp-site-blocks) > :first-child { margin-block-start: 0; }:where(.wp-site-blocks) > :last-child { margin-block-end: 0; }:root { --wp--style--block-gap: ; }.is-layout-flow  > :first-child{margin-block-start: 0;}.is-layout-flow  > :last-child{margin-block-end: 0;}.is-layout-flow  > *{margin-block-start: 1;margin-block-end: 0;}.is-layout-constrained  > :first-child{margin-block-start: 0;}.is-layout-constrained  > :last-child{margin-block-end: 0;}.is-layout-constrained  > *{margin-block-start: 1;margin-block-end: 0;}.is-layout-flex {gap: 1;}.is-layout-grid {gap: 1;}.is-layout-flow > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-flow > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-flow > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > .alignleft{float: left;margin-inline-start: 0;margin-inline-end: 2em;}.is-layout-constrained > .alignright{float: right;margin-inline-start: 2em;margin-inline-end: 0;}.is-layout-constrained > .aligncenter{margin-left: auto !important;margin-right: auto !important;}.is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){margin-left: auto !important;margin-right: auto !important;}body .is-layout-flex{display: flex;}.is-layout-flex{flex-wrap: wrap;align-items: center;}.is-layout-flex > :is(*, div){margin: 0;}body .is-layout-grid{display: grid;}.is-layout-grid > :is(*, div){margin: 0;}';
-		$this->assertSame( $expected, $theme_json->get_root_layout_rules( WP_Theme_JSON_Gutenberg::ROOT_BLOCK_SELECTOR, $metadata ) );
+		$this->assertSameCSS( $expected, $theme_json->get_root_layout_rules( WP_Theme_JSON_Gutenberg::ROOT_BLOCK_SELECTOR, $metadata ) );
 	}
 
 	public function test_sanitization() {
@@ -4717,8 +4757,8 @@ public function test_shadow_preset_styles() {
 		);
 
 		$expected_styles = ':root{--wp--preset--shadow--natural: 5px 5px 5px 0 black;--wp--preset--shadow--sharp: 5px 5px black;}';
-		$this->assertSame( $expected_styles, $theme_json->get_stylesheet(), 'Styles returned from "::get_stylesheet()" does not match expectations' );
-		$this->assertSame( $expected_styles, $theme_json->get_stylesheet( array( 'variables' ) ), 'Styles returned from "::get_stylesheet()" when requiring "variables" type does not match expectations' );
+		$this->assertSameCSS( $expected_styles, $theme_json->get_stylesheet(), 'Styles returned from "::get_stylesheet()" does not match expectations' );
+		$this->assertSameCSS( $expected_styles, $theme_json->get_stylesheet( array( 'variables' ) ), 'Styles returned from "::get_stylesheet()" when requiring "variables" type does not match expectations' );
 	}
 
 	public function test_get_shadow_styles_for_blocks() {
@@ -4756,7 +4796,7 @@ public function test_get_shadow_styles_for_blocks() {
 		$variable_styles = ':root{--wp--preset--shadow--natural: 5px 5px 0 0 black;}';
 		$element_styles  = 'a:where(:not(.wp-element-button)){box-shadow: var(--wp--preset--shadow--natural);}:root :where(.wp-element-button, .wp-block-button__link){box-shadow: var(--wp--preset--shadow--natural);}:root :where(p){box-shadow: var(--wp--preset--shadow--natural);}';
 		$expected_styles = $variable_styles . $element_styles;
-		$this->assertSame( $expected_styles, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
+		$this->assertSameCSS( $expected_styles, $theme_json->get_stylesheet( array( 'styles', 'presets', 'variables' ), null, array( 'skip_root_layout_styles' => true ) ) );
 	}
 
 	public function test_get_top_level_background_image_styles() {
@@ -4783,7 +4823,7 @@ public function test_get_top_level_background_image_styles() {
 		);
 
 		$expected_styles = "html{min-height: calc(100% - var(--wp-admin--admin-bar--height, 0px));}body{background-image: url('http://example.org/image.png');background-position: center center;background-repeat: no-repeat;background-size: contain;background-attachment: fixed;}";
-		$this->assertSame( $expected_styles, $theme_json->get_styles_for_block( $body_node ), 'Styles returned from "::get_styles_for_block()" with top-level background styles do not match expectations' );
+		$this->assertSameCSS( $expected_styles, $theme_json->get_styles_for_block( $body_node ), 'Styles returned from "::get_styles_for_block()" with top-level background styles do not match expectations' );
 
 		$theme_json = new WP_Theme_JSON_Gutenberg(
 			array(
@@ -4801,7 +4841,7 @@ public function test_get_top_level_background_image_styles() {
 		);
 
 		$expected_styles = "html{min-height: calc(100% - var(--wp-admin--admin-bar--height, 0px));}body{background-image: url('http://example.org/image.png');background-position: center center;background-repeat: no-repeat;background-size: contain;background-attachment: fixed;}";
-		$this->assertSame( $expected_styles, $theme_json->get_styles_for_block( $body_node ), 'Styles returned from "::get_styles_for_block()" with top-level background image as string type do not match expectations' );
+		$this->assertSameCSS( $expected_styles, $theme_json->get_styles_for_block( $body_node ), 'Styles returned from "::get_styles_for_block()" with top-level background image as string type do not match expectations' );
 	}
 
 	public function test_get_block_background_image_styles() {
@@ -4844,7 +4884,7 @@ public function test_get_block_background_image_styles() {
 		);
 
 		$quote_styles = ":root :where(.wp-block-quote){background-image: url('http://example.org/quote.png');background-position: center center;background-repeat: no-repeat;background-size: cover;}";
-		$this->assertSame( $quote_styles, $theme_json->get_styles_for_block( $quote_node ), 'Styles returned from "::get_styles_for_block()" with block-level background styles do not match expectations' );
+		$this->assertSameCSS( $quote_styles, $theme_json->get_styles_for_block( $quote_node ), 'Styles returned from "::get_styles_for_block()" with block-level background styles do not match expectations' );
 
 		$group_node = array(
 			'name'      => 'core/group',
@@ -4856,7 +4896,7 @@ public function test_get_block_background_image_styles() {
 		);
 
 		$group_styles = ":root :where(.wp-block-group){background-image: url('http://example.org/group.png');background-position: center center;background-repeat: no-repeat;background-size: cover;background-attachment: fixed;}";
-		$this->assertSame( $group_styles, $theme_json->get_styles_for_block( $group_node ), 'Styles returned from "::get_styles_for_block()" with block-level background styles as string type do not match expectations' );
+		$this->assertSameCSS( $group_styles, $theme_json->get_styles_for_block( $group_node ), 'Styles returned from "::get_styles_for_block()" with block-level background styles as string type do not match expectations' );
 	}
 
 	/**