[scss mode] Allow interpolation inside braces

mode/css/css.js

@@ -239,6 +239,7 @@ CodeMirror.defineMode("css", function(config, parserConfig) {
     if (type == "{" || type == "}") return popAndPass(type, stream, state);
     if (type == ")") return popContext(state);
     if (type == "(") return pushContext(state, stream, "parens");
+    if (type == "interpolation") return pushContext(state, stream, "interpolation");
     if (type == "word") wordAsValue(stream);
     return "parens";
   };