Add Text Decoration

Does anyone know how to add this text decoration?  Thanks in advance!

Add a Code Block > Paste this code

<h1><span>Heading 1</span></h1>
<style>
 h1 span {
   position: relative;
         }
  h1 span:after {
    content: "";
    background-color: yellow;
    position: absolute;
    bottom: 0px;
    height: 40px;
    width: 100%;
    left: 50%;
    transform: translateX(-50%);
    z-index: -1;
  }

</style>