Convert theme to TS

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/@types/global.d.ts

@@ -159,6 +159,10 @@ declare global {
         setSinkId(outputId: string);
     }
 
+    interface HTMLStyleElement {
+        disabled?: boolean;
+    }
+
     // Add Chrome-specific `instant` ScrollBehaviour
     type _ScrollBehavior = ScrollBehavior | "instant";