docs(theming) update theme.config override example (#4174)

* Update Theming.mdx

* Update docs/src/pages/Theming.mdx

Co-authored-by: Oleksandr Fediashov <alexander.mcgarret@gmail.com>

Co-authored-by: Oleksandr Fediashov <alexander.mcgarret@gmail.com>

docs/src/pages/Theming.mdx

@@ -153,7 +153,11 @@ This file is mostly prepared, but you have to change some details in the bottom
 @themesFolder : 'themes';
 @siteFolder  : '../../src/semantic-ui/site';
 
-@import (multiple) "~semantic-ui-less/theme.less";
+/*******************************
+         Import Theme
+*******************************/
+
+@import (multiple) '~semantic-ui-less/theme.less';
 @fontPath : '../../../themes/@{theme}/assets/fonts';
 ```