Edit in JSFiddle

debugCSS({

});

/*! mercury.css v1.0 | MIT License | https://github.com/wmeredith/MercuryCSS */
html {
  font-family: "Georgia", serif;
  font-size: 62.5%; }

body {
  background-color: #FBFBFB;
  color: #222;
  font-size: 1.618rem;
  font-weight: 400;
  line-height: 1.325;
  margin: auto;
  max-width: 90%;
  padding: 1.325;
  width: 42em; }

h1, h2, h3, h4, h5, th, h6 {
  hyphens: auto;
  overflow-wrap: break-word;
  word-wrap: break-word;
  -ms-word-break: break-all;
  word-break: break-word;
  -ms-hyphens: auto;
  -moz-hyphens: auto;
  -webkit-hyphens: auto;
  font-family: "Verdana", sans-serif;
  font-weight: 600;
  letter-spacing: .05em;
  line-height: 1.325;
  margin: .66em 0 0; }

h1 {
  font-size: 4.98703rem; }

h2 {
  font-size: 3.7638rem; }

h3 {
  font-size: 2.8406rem; }

h4 {
  font-size: 2.14385rem; }

h5, th {
  font-size: 1.618rem; }

h6 {
  font-size: 1.22113rem; }

small, sub, sup, caption {
  font-size: 1.22113rem;
  font-weight: 400;
  letter-spacing: 0; }

a {
  border-bottom: 1px dotted #1F5AFF;
  color: #1F5AFF;
  text-decoration: none; }
  a:hover {
    border-bottom: 1px solid #1F5AFF; }
  a:visited {
    border-bottom: 1px dotted #9D32FF;
    color: #9D32FF; }

p, fieldset {
  margin-bottom: 1.325em; }

b, strong {
  font-weight: 600; }

i, em {
  font-style: italic; }

ul, ol {
  padding-left: 2.65em; }
  ul ul, ul ol, ol ul, ol ol {
    padding-bottom: 0;
    padding-top: 0.6625em; }

li {
  margin-bottom: 0.6625em; }

blockquote {
  border-left: 1px solid #919191;
  margin-bottom: 1.325em;
  margin-left: 0.6625em;
  padding-left: 1.325em; }

hr {
  border: 0;
  border-top: 1px solid #919191; }

pre {
  background-color: #eaeaea;
  color: #000;
  display: block;
  overflow-x: auto;
  padding: 1.325em; }

code {
  color: #000;
  white-space: pre-wrap; }

pre > code {
  background-color: transparent;
  padding: 0;
  white-space: pre; }

img {
  max-width: 100%; }

table {
  border-collapse: collapse;
  text-align: justify;
  width: 100%; }

th {
  border-bottom: 1px solid #919191;
  font-family: "Verdana", sans-serif;
  padding: 0.6625em 0.6625em; }

td {
  padding: 0.44167em 0.6625em; }

tbody tr {
  border-bottom: 1px solid #d5d5d5; }
  tbody tr:last-of-type {
    border: 0; }

input, textarea {
  border: 1px solid #222; }
  input:focus, textarea:focus {
    border: 1px solid #1F5AFF; }

textarea {
  width: 100%; }

textarea, select, input[type] {
  color: #222;
  padding: 0.44167em;
  margin-bottom: 0.6625em;
  background-color: #FFF;
  border: 1px solid #eaeaea;
  border-radius: 2px;
  box-shadow: 0;
  box-sizing: border-box; }
  textarea:focus, select:focus, input[type]:focus {
    border: 1px solid #1F5AFF;
    outline: 0; }

input:invalid {
  border: 1px solid #FC2B07;
  outline: 0; }

label, legend, fieldset {
  display: block; }

label {
  margin-bottom: 0.33125em; }

fieldset {
  border-radius: 4px;
  box-shadow: 0 2px 3px -1px rgba(34, 34, 34, 0.1); }

.button, button, input[type="submit"], input[type="reset"], input[type="button"] {
  background-color: #4878ff;
  border: 1px solid #0446ff;
  border-radius: 4px;
  box-shadow: 0 3px 4px -2px rgba(34, 34, 34, 0.5);
  box-sizing: border-box;
  color: #FFF;
  cursor: pointer;
  display: inline-block;
  padding: 0.44167em 0.6625em;
  text-align: center;
  text-decoration: none;
  text-transform: uppercase;
  white-space: nowrap; }
  .button:focus, .button:hover, button:focus, button:hover, input[type="submit"]:focus, input[type="submit"]:hover, input[type="reset"]:focus, input[type="reset"]:hover, input[type="button"]:focus, input[type="button"]:hover {
    background-color: #2d64ff;
    border-color: #0032bf;
    outline: 0; }
  .button[disabled], button[disabled], input[type="submit"][disabled], input[type="reset"][disabled], input[type="button"][disabled] {
    box-shadow: none;
    cursor: default;
    opacity: .5; }
    .button[disabled]:hover, button[disabled]:hover, input[type="submit"][disabled]:hover, input[type="reset"][disabled]:hover, input[type="button"][disabled]:hover {
      background-color: #4878ff;
      border-color: #1f5aff;
      cursor: default; }

<nav>
  <ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Clients</a></li>
    <li><a href="#">Contact Us</a></li>
  </ul>
</nav>
<p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.</p>
<ol>
  <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
  <li>Aliquam tincidunt mauris eu risus.</li>
  <li>Vestibulum auctor dapibus neque.</li>
</ol>
<h1>HTML Ipsum Presents</h1>

<p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em> Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>

<h2>Header Level 2</h2>

<ol>
  <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
  <li>Aliquam tincidunt mauris eu risus.</li>
</ol>

<blockquote>
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis elit sit amet quam. Vivamus pretium ornare est.</p>
</blockquote>

<h3>Header Level 3</h3>

<ul>
  <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
  <li>Aliquam tincidunt mauris eu risus.</li>
</ul>

<pre><code>
#header h1 a {
  display: block;
  width: 300px;
  height: 80px;
}
</code></pre>