reuse scss variables in js for SSOT (#2867)

src/css/styles.scss

@@ -1,4 +1,4 @@
-@import "./_variables";
+@import "./variables.module";
 @import "./theme";
 
 .excalidraw {

src/css/variables.module.scss

@@ -2,3 +2,7 @@
 
 // keep up to date with is-mobile.tsx
 $is-mobile-query: "(max-width: 600px), (max-height: 500px) and (max-width: 1000px)";
+
+:export {
+  isMobileQuery: unquote($is-mobile-query);
+}