// source https://jsbin.com

index.html

<style id="jsbin-css">
* {
    border: 1px solid black;
}
div {
    background: red; 
    margin: 30px;
}
section {
    margin: 20px;
    padding: 30px;
    background: orange; 
}
h1, p {
    padding: 8px;
    /* or simply */
    background-color: yellow; 
}


<script id="jsbin-source-html" type="text/html"><div>
  <section>
      <h1> a title </h1>
      <p> paragraph </p>
   </section>
</div>
</script>

<script id="jsbin-source-css" type="text/css">* {
    border: 1px solid black;
}
div {
    background: red; 
    margin: 30px;
}
section {
    margin: 20px;
    padding: 30px;
    background: orange; 
}
h1, p {
    padding: 8px;
    /* or simply */
    background-color: yellow; 
}

</body>
</html></script>
</body>
</html>
</style>
<div>
  <section>
      <h1> a title </h1>
      <p> paragraph </p>
   </section>
</div>

jsbin.untitled.css

* {
    border: 1px solid black;
}
div {
    background: red; 
    margin: 30px;
}
section {
    margin: 20px;
    padding: 30px;
    background: orange; 
}
h1, p {
    padding: 8px;
    /* or simply */
    background-color: yellow; 
}

</body>
</html>