JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
      <title>My test page</title>
     <link rel="stylesheet" type="text/css" href="CSS\Style.css">
  </head>
  <body>

     <header>
       Зюзька
     </header>

        <div>
          <aside>
            масяка
          </aside>

          <main>
            плюк
          </main>
        </div>
   
    <footer>
      зюзь
    </footer>

  </body>
</html>

CSS

header {background-color: green; 
        width: 900px; 
          height: 100px; 
        text-align: center; 
         padding-top: 30px; 
         margin: 10px auto;
          }
          div {width: 900px; 
            margin: 10px auto}
          aside {background-color: yellow; 
            height: 300px; 
            text-align: center; 
            padding-top: 30px; 
            width: 300px; float: left;}
          main{background-color: orange; 
            height: 300px; 
            text-align: center; 
            padding-top: 30px;}
          footer {background-color: pink; 
            width: 900px; 
            height: 100px; 
            text-align: center; 
            padding-top: 30px; 
            margin: 10px auto;}