prettier/tests/html_css/less.html

<style type="text/less">
  @nice-blue: #5B83AD;
  @light-blue: @nice-blue + #111;

  #header {
    color: @light-blue;
  }
</style>

<style lang="less">
  @nice-blue: #5B83AD;
  @light-blue: @nice-blue + #111;

  #header {
    color: @light-blue;
  }
</style>