HTML<button>Press Me!</button>

CSSbutton {
    width:20px;
    height:28px;
    color:#fff;
    font-size:28px;
    padding:11px 15px;
    border-radius:5px;
    background:#14ADE5;
  }

JS<button onclick="myFunction()">Post</button>
  
  <script>
  function myFunction() {
      document.write(5 + 6);
  }
  </script>

Jquery$(document).ready(function{
   jQuery.cssRule(".post", "display", "block");
  });