Hello world

body {
  background: red;
}

@width: 10px;
@height: @width + 10px;

#header {
  width: @width;
  height: @height;
}

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
</body>
</html>

console.log("foo");