JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
  <head>
  </head>
  <body>
      <header id="sidebar">
         blablabla
      </header>
      <section id="main">
         <h1>Gotcha!</h1>
      </section>
  </body>
</html>

CSS

html,body {
            margin:0;
            padding:0;
            width:100%;
            height:100%;
          }
 
          #sidebar {
            display:block;
            position:absolute;
            width:25%;
            min-height:100%;
            border-right:1px solid #222;
            background-color: #E0E0E0;
          }

          #main {
            margin-left:25%;
            display:block;
          }

          h1 {
            padding:2%;
            /* margin:0; */
            /* defining the margin as zero aligns 
             * everything at the top */
          }