Override the default styling of .highlight in the editor.

Closes #4136

static/text-editor-light.less

@@ -11,3 +11,9 @@ atom-text-editor.mini {
   line-height: @component-line-height;
   max-height: @component-line-height + 2; // +2 for borders
 }
+
+// TODO: remove this when the shadow DOM is the default
+atom-text-editor .highlight {
+  background: none;
+  padding: 0;
+}

static/text-editor-shadow.less

@@ -244,11 +244,6 @@
   width: 1px;
 }
 
-.highlight {
-  background: none;
-  padding: 0;
-}
-
 .highlight .region,
 .selection .region {
   position: absolute;