[Preview] Highlight expression yellow firefox-devtools#2984 (firefox-devtools#3022)

* [Preview] Highlight expression yellow firefox-devtools#2984

* Now using theme-highlight-yellow variable after resolving firefox-devtools/devtools-core#385 (firefox-devtools#2984)

Author: ofiron01

src/components/Editor/Preview.css

@@ -28,7 +28,7 @@
 }
 
 .selected-token {
-  background-color: var(--theme-search-overlays-semitransparent);
+  background-color: var(--theme-highlight-yellow);
   color: var(--theme-selection-color);
 }