Nostalgia always work. Do you remember blue screens of death (BSOD)? A blue page happens when your (old) computer turned off suddenly because of deadly error. You can catch this idea and build a simple 404 not found page!


HTML
<!-- This script got from www.devanswer.com -->
<main class="bsod container">
<h1 class="neg title"><span class="bg">Error - 404</span></h1>
<p>An error has occured, to continue:</p>
<p>* Return to our homepage.<br />
* Send us an e-mail about this error and try later.</p>
<nav class="nav">
<a href="#" class="link">index</a> | <a href="#" class="link">webmaster</a>
</nav>
</main><div id="bcl"><a style="font-size:8pt;text-decoration:none;" href="http://www.devanswer.com">Developers Answer</a></div>
                        

CSS
@import "https://fonts.googleapis.com/css?family=VT323";
body,
h1,
h2,
h3,
h4,
p,
a {
  color: #e0e2f4;
}

body,
p {
  font: normal 20px/1.25rem "VT323", monospace;
}

h1 {
  font: normal 2.75rem/1.05em "VT323", monospace;
}

h2 {
  font: normal 2.25rem/1.25em "VT323", monospace;
}

h3 {
  font: lighter 1.5rem/1.25em "VT323", monospace;
}

h4 {
  font: lighter 1.125rem/1.2222222em "VT323", monospace;
}

body {
  background: #0414a7;
}

.container {
  width: 90%;
  margin: auto;
  max-width: 640px;
}

.bsod {
  padding-top: 10%;
}
.bsod .neg {
  text-align: center;
  color: #0414a7;
}
.bsod .neg .bg {
  background: #aaaaaa;
  padding: 0 15px 2px 13px;
}
.bsod .title {
  margin-bottom: 50px;
}
.bsod .nav {
  margin-top: 35px;
  text-align: center;
}
.bsod .nav .link {
  text-decoration: none;
  padding: 0 9px 2px 8px;
}
.bsod .nav .link:hover, .bsod .nav .link:focus {
  background: #aaaaaa;
  color: #0414a7;
}