diff --git a/layout/style/res/plaintext.css b/layout/style/res/plaintext.css
index d74e764a57e4..04d9b500b188 100644
--- a/layout/style/res/plaintext.css
+++ b/layout/style/res/plaintext.css
@@ -18,17 +18,8 @@ html:not([dir]) pre { /* Not a UA sheet, so doesn't use :-moz-has-dir-attr */
 }
 
 @-moz-document unobservable-document() {
-  @media (prefers-color-scheme: dark) {
-    :root {
-      /**
-       * in-content-page-{color, background} for dark theme.
-       *
-       * TODO(emilio): Make this just `color-scheme: dark` once color-scheme ships,
-       * (or `color-scheme: light dark` outside the media query).
-       */
-      background: rgb(28,27,34);
-      color: rgb(251,251,254);
-    }
+  :root {
+    color-scheme: light dark;
   }
 }
 
diff --git a/toolkit/themes/shared/in-content/common.inc.css b/toolkit/themes/shared/in-content/common.inc.css
index ded3373d3f51..983983cdafc6 100644
--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -119,7 +119,6 @@
   :root {
     /* Keep these in sync with:
      *
-     *  * plaintext.css
      *  * nsXPLookAndFeel::GenericDarkColor
      *  * The default value of browser.display.foreground_color.dark and
      *    browser.display.background_color.dark