--- a/browser/themes/addons/alpenglow/manifest.json
+++ b/browser/themes/addons/alpenglow/manifest.json
@@ -59,17 +59,18 @@
       "popup": "hsla(254, 46%, 21%, 1)",
       "popup_text": "hsla(255, 100%, 94%, 1)",
       "popup_border": "hsla(255, 100%, 94%, .32)",
       "popup_highlight": "hsla(255, 100%, 94%, .12)",
       "sidebar": "hsla(240, 15%, 95%, 1)",
       "sidebar_text": "hsla(261, 53%, 15%, 1)",
       "sidebar_border": "hsla(261, 53%, 15%, .24)",
       "sidebar_highlight": "hsla(265, 100%, 72%, 1)",
-      "sidebar_highlight_text": "hsla(0, 0%, 100%, 1)"
+      "sidebar_highlight_text": "hsla(0, 0%, 100%, 1)",
+      "focus_outline": "hsla(258, 65%, 48%, 1)"
     }
   },
   "dark_theme": {
     "images": {
       "additional_backgrounds": [
         "background-noodles-right-dark.svg",
         "background-noodles-left-dark.svg",
         "background-gradient-dark.svg"
@@ -114,12 +115,19 @@
       "popup": "hsla(250, 43%, 25%, 1)",
       "popup_text": "hsla(255, 100%, 94%, 1)",
       "popup_border": "hsla(255, 100%, 94%, .32)",
       "popup_highlight": "hsla(255, 100%, 94%, .12)",
       "sidebar": "hsla(250, 43%, 25%, 1)",
       "sidebar_text": "hsla(255, 100%, 94%, 1)",
       "sidebar_border": "hsla(255, 100%, 94%, .24)",
       "sidebar_highlight": "hsla(259, 76%, 58%, 1)",
-      "sidebar_highlight_text": "hsla(0, 0%, 100%, 1)"
+      "sidebar_highlight_text": "hsla(0, 0%, 100%, 1)",
+      "focus_outline": "hsla(265, 100%, 72%, 1)"
+    }
+  },
+
+  "theme_experiment": {
+    "colors": {
+      "focus_outline": "--focus-outline-color"
     }
   }
 }

--- a/toolkit/components/extensions/parent/ext-theme.js
+++ b/toolkit/components/extensions/parent/ext-theme.js
@@ -63,16 +63,23 @@ class Theme {
 
       if (experiment) {
         if (extension.experimentsAllowed) {
           this.lwtStyles.experimental = {
             colors: {},
             images: {},
             properties: {},
           };
+          if (this.lwtDarkStyles) {
+            this.lwtDarkStyles.experimental = {
+              colors: {},
+              images: {},
+              properties: {},
+            };
+          }
           const { baseURI } = this.extension;
           if (experiment.stylesheet) {
             experiment.stylesheet = baseURI.resolve(experiment.stylesheet);
           }
           this.experiment = experiment;
         } else {
           const { logger } = this.extension;
           logger.warn("This extension is not allowed to run theme experiments");