Remove text opacity CSS variables from ::marker (#8622)

* Refactor

* Allow parallel variant fns to mutate the container

* Remove text color variable from marker pseudo class

wip

* Update changelog

src/util/removeAlphaVariables.js

@@ -0,0 +1,24 @@
+/**
+ * This function removes any uses of CSS variables used as an alpha channel
+ *
+ * This is required for selectors like `:visited` which do not allow
+ * changes in opacity or external control using CSS variables.
+ *
+ * @param {import('postcss').Container} container
+ * @param {string[]} toRemove
+ */
+export function removeAlphaVariables(container, toRemove) {
+  container.walkDecls((decl) => {
+    if (toRemove.includes(decl.prop)) {
+      decl.remove()
+
+      return
+    }
+
+    for (let varName of toRemove) {
+      if (decl.value.includes(`/ var(${varName})`)) {
+        decl.value = decl.value.replace(`/ var(${varName})`, '')
+      }
+    }
+  })
+}