diff --git a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-alpha.html b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-alpha.html
new file mode 100644
index 000000000000..1e7bd12eb491
--- /dev/null
+++ b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-alpha.html
@@ -0,0 +1,181 @@
+<
+!
+doctype
+html
+>
+<
+title
+>
+CSS
+Color
+Adjustment
+Test
+:
+iframe
+element
+with
+light
+color
+-
+scheme
+frame
+document
+with
+dark
+color
+-
+scheme
+:
+root
+background
+with
+alpha
+<
+/
+title
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+color
+-
+adjust
+/
+#
+color
+-
+scheme
+-
+effect
+"
+>
+<
+link
+rel
+=
+"
+match
+"
+href
+=
+"
+support
+/
+dark
+-
+frame
+-
+alpha
+.
+html
+"
+>
+<
+link
+rel
+=
+"
+stylesheet
+"
+href
+=
+"
+support
+/
+assert
+-
+preferred
+-
+dark
+.
+css
+"
+>
+<
+style
+>
+html
+body
+{
+margin
+:
+0
+;
+height
+:
+100
+%
+;
+}
+iframe
+{
+margin
+:
+0
+;
+border
+:
+0
+;
+padding
+:
+0
+;
+width
+:
+100
+%
+;
+height
+:
+100
+%
+;
+display
+:
+block
+;
+}
+<
+/
+style
+>
+<
+iframe
+src
+=
+"
+support
+/
+dark
+-
+frame
+-
+alpha
+.
+html
+"
+>
+<
+/
+iframe
+>
diff --git a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-opaque.html b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-opaque.html
new file mode 100644
index 000000000000..9ff8a855e511
--- /dev/null
+++ b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background-mismatch-opaque.html
@@ -0,0 +1,186 @@
+<
+!
+doctype
+html
+>
+<
+title
+>
+CSS
+Color
+Adjustment
+Test
+:
+Frames
+with
+a
+dark
+color
+-
+scheme
+should
+get
+an
+opaque
+background
+when
+embedding
+element
+and
+embedded
+root
+color
+-
+schemes
+do
+not
+match
+<
+/
+title
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+color
+-
+adjust
+/
+#
+color
+-
+scheme
+-
+effect
+"
+>
+<
+link
+rel
+=
+"
+match
+"
+href
+=
+"
+support
+/
+dark
+-
+frame
+-
+opaque
+.
+html
+"
+>
+<
+link
+rel
+=
+"
+stylesheet
+"
+href
+=
+"
+support
+/
+assert
+-
+preferred
+-
+dark
+.
+css
+"
+>
+<
+style
+>
+html
+body
+{
+margin
+:
+0
+;
+height
+:
+100
+%
+;
+}
+iframe
+{
+margin
+:
+0
+;
+border
+:
+0
+;
+padding
+:
+0
+;
+width
+:
+100
+%
+;
+height
+:
+100
+%
+;
+display
+:
+block
+;
+}
+<
+/
+style
+>
+<
+iframe
+src
+=
+"
+support
+/
+dark
+-
+frame
+-
+opaque
+.
+html
+"
+>
+<
+/
+iframe
+>
diff --git a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background.html b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background.html
index 50e04ec05697..4e712212c8fa 100644
--- a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background.html
+++ b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/color-scheme-iframe-background.html
@@ -22,6 +22,16 @@
 still
 be
 transparent
+when
+embedding
+element
+and
+embedded
+root
+color
+-
+schemes
+match
 <
 /
 title
@@ -57,7 +67,7 @@
 -
 scheme
 -
-processing
+effect
 "
 >
 <
@@ -116,6 +126,15 @@
 "
 400
 "
+style
+=
+"
+color
+-
+scheme
+:
+dark
+"
 src
 =
 "
diff --git a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-alpha.html b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-alpha.html
new file mode 100644
index 000000000000..de045edb41a9
--- /dev/null
+++ b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-alpha.html
@@ -0,0 +1,66 @@
+<
+!
+doctype
+html
+>
+<
+style
+>
+:
+root
+{
+color
+-
+scheme
+:
+dark
+;
+background
+-
+color
+:
+rgba
+(
+0
+128
+0
+0
+.
+5
+)
+;
+}
+p
+{
+color
+:
+lime
+}
+<
+/
+style
+>
+<
+p
+>
+This
+text
+should
+be
+lime
+and
+the
+background
+should
+be
+green
+blended
+with
+a
+dark
+canvas
+.
+<
+/
+p
+>
diff --git a/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-opaque.html b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-opaque.html
new file mode 100644
index 000000000000..f7075339c467
--- /dev/null
+++ b/testing/web-platform/tests/css/css-color-adjust/rendering/dark-color-scheme/support/dark-frame-opaque.html
@@ -0,0 +1,47 @@
+<
+!
+doctype
+html
+>
+<
+style
+>
+:
+root
+{
+color
+-
+scheme
+:
+dark
+}
+p
+{
+color
+:
+green
+}
+<
+/
+style
+>
+<
+p
+>
+This
+text
+should
+be
+green
+and
+the
+background
+should
+be
+dark
+opaque
+.
+<
+/
+p
+>