feat: Support dark mode in login pages (#7420)

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/javascript/shared/components/Spinner.vue

@@ -1,5 +1,5 @@
 <template>
-  <span class="spinner" :class="`${size} ${colorScheme}`" />
+  <span class="spinner" :class="`${size} ${colorSchemeClasses}`" />
 </template>
 <script>
 export default {
@@ -13,6 +13,15 @@ export default {
       default: '',
     },
   },
+  computed: {
+    colorSchemeClasses() {
+      if (this.colorScheme === 'primary') {
+        return 'before:!border-t-woot-500';
+      }
+
+      return this.colorScheme;
+    },
+  },
 };
 </script>
 <style scoped lang="scss">