<!doctype html>
<meta charset=utf-8>
<meta name="viewport" content="width=device-width">
<style>
  body {
    margin: 0;
  }
  .fixed {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 50px;
    background-color: blue;
  }
</style>
<div class="fixed"></div>
