Just add the line
<script src="https://gistcdn.githack.com/easrng/c7f6d9062215782cef74b12183f6392b/raw/6d5ec912dee98e5b999373149ca36c10a9b64900/cssmixin.js" defer></script>
to the bottom of your <head>
tag.
Mixins are 100% valid CSS. To declare a mixin, make a rule with the selector
[--mixin="your-mixin-name"]. To use a mixin, use the rule
--mixins:mixin-name-1 mixin-name-2;
For performance info, see our benchmark page, here.
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