how to use id and class in html code example

Example 1: how to call an id in css

<style>
  #selector {
  color: red;
}
/* # is id selector */
</style>


<div id="selector">
<p>This is an id</p>
</div>

Example 2: referance html id css

<style>
  #test {
  /*Styleing here*/
  }
</style>
<h1 id="test"></h1>