JSFiddle - React, Tailwind, and code Playground

HTML

<html>

  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Home</title>
    <link rel="stylesheet" type="text/CSS" href="style.css">
  </head>

  <body>
    <div id="header">
      Header
    </div>


    <div id="sidebar">
    </div>

    <div id="main">
      <div class="col-3">
      </div>
      <div class="col-3">
      </div>
      <div class="col-3">
      </div>
      <div class="col-3">
      </div>
    </div>

    <div id="footer">
      <p>Copyright 2016 Ubedz Scumbag</p>
    </div>
  </body>

</html>

CSS

* {
  margin: 0;
  width: 100%;
}

#header {
  background-color: #1abc9c;
  height: 20%;
  width: 100%;
}

#sidebar {
  height: 75%;
  width: 20%;
  float: left;
  background-color: #16a085;
}

#main {
  height: 75%;
  width: 80%;
  float: left;
}

.col-3 {
  height: 40%;
  width: 23%;
  margin: 1%;
  background-color: yellow;
  float: left;
}

#footer {
  height: 5%;
  width: 100%;
  background-color: #1abc9c;
  clear: left;
}

@media (max-width: 500px) {
  #header {
    background-color: red;
  }
}