W3Schools Tryit Editor

mystyle.scss

mystyle.css

mypage.html

@mixin important-text {
  color: red;
  font-size: 25px;
  font-weight: bold;
  border: 1px solid blue;
}

.danger {
  @include important-text;
  background-color: green;
}

.danger {
  color: red;
  font-size: 25px;
  font-weight: bold;
  border: 1px solid blue;
  background-color: green;
}

<!DOCTYPE html>
<html>
<link rel="stylesheet" href="mystyle.css">
<body>

<h1>Hello World</h1>

<p class="danger">Warning! This is some text.</p>

</body>
</html>