build: keep selector list in dist output of not pseudo-class (#2740)

A change in configuration had resulted in some regressions due to
increased specificity created in the dist output of :not selectors.
One issue was with a disabled Menu item showing a change in icon color
on hover.

The config override being removed here sets it back to the default
stage 2 configuration that allows multiple comma separated selectors
within :not(). The configuration had been converting each item in the
:not selector list into its own :not selector, increasing specificity
for each additional item.

.changeset/eight-spiders-help.md

@@ -0,0 +1,11 @@
+---
+"@spectrum-css/calendar": patch
+"@spectrum-css/combobox": patch
+"@spectrum-css/datepicker": patch
+"@spectrum-css/menu": patch
+"@spectrum-css/picker": patch
+"@spectrum-css/slider": patch
+"@spectrum-css/stepper": patch
+---
+
+Build change to remove the `postcss-preset-env` polyfill for the dist output of `:not` selectors containing multiple selectors, to avoid an unintended increase in specificity, which caused some visual regressions.

postcss.config.js

@@ -118,7 +118,6 @@ module.exports = ({
 					// https://github.com/jsxtools/focus-within
 					"focus-within-pseudo-class": true,
 					"font-format-keywords": true,
-					"not-pseudo-class": true,
 					"opacity-percentage": true,
 					// https://github.com/csstools/postcss-plugins/tree/main/plugins/css-prefers-color-scheme
 					"prefers-color-scheme-query": true,