feat(admin): refine theme settings UI

assets/admin/src/components/EmptyState.vue

@@ -28,20 +28,20 @@ defineProps({
 
 .aksrt-empty-state__icon {
   margin-bottom: 20px;
-  color: #c0c4cc;
+  color: var(--aksrt-color-border-strong);
 }
 
 .aksrt-empty-state__title {
   margin: 0 0 8px;
   font-size: 18px;
   font-weight: 600;
-  color: #1a1a2e;
+  color: var(--aksrt-color-text);
 }
 
 .aksrt-empty-state__desc {
   margin: 0;
   font-size: 13px;
-  color: #7a7f8a;
+  color: var(--aksrt-color-muted);
   max-width: 360px;
   line-height: 1.65;
 }