LESS for JSFiddle

Compile LESS to CSS in JSFiddle

On JSFiddle, add a Resources.

Link to the LESS CDN: https://cdnjs.cloudflare.com/ajax/libs/less.js/1.6.3/less.min.js.

In the Styles pane, change the style sheet language to SCSS.

In the Scripts pane, change the script to JavaScript - No Libraries

Paste the below JavaScript:

var arr = document.getElementsByTagName("style")
for (var i = 0; i < arr.length; i++) {
  if (arr[i].type == 'text/css') arr[i].setAttribute('type', 'text/less')
}
less.env = 'development'
less.refreshStyles()

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See it in action: https://jsfiddle.net/timhjellum/m0r13wfc/41/.