<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  
  <div class='normal'>I'm a default size text.</div>
  <div class='doubled'>My size has been doubled.</div>
  <div class='biggest'>I'm the biggest</div>
  
</body>
</html>
$size: 4em;

@function setFontSize($newSize: 1em) {
  @return $newSize;
}

@function doubleFontSize($newSize: 1em) {
  @return $newSize * 2;
}

.normal {
  font-size: setFontSize();
  color: red;
}

.biggest {
    font-size: setFontSize($size);
    color: green;
}

.doubled {
  font-size: doubleFontSize();
  color: blue;
}
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