<a class="skip-main" href="#main">Skip to main content</a>
<nav>
  <ul>
    <li><a href="#">Nav Item 1</a></li>
    <li><a href="#">Nav Item 2</a></li>
    <li><a href="#">Nav Item 3</a></li>
    <li><a href="#">Nav Item 4</a></li>
  </ul>
</nav>
<main id="main" tabindex="-1">
  <h1><a href="#">Title</a></h1>
  <p>First paragraph with <a href="#">some</a> <a href="#">links</a></p>
  <p>Second paragraph with <a href="#">some</a> <a href="#">other</a> <a href="#">links</a></p>
</main>

body {
  background: #f2f2f2;
  padding: 30px;
}
a.skip-main {
  left: -999px;
  position: absolute;
  top: auto;
  width: 1px;
  height: 1px;
  overflow: hidden;
  z-index: -999;
}
a.skip-main:focus {
  left: auto;
  top: auto;
  width: 30%;
  height: auto;
  overflow: auto;
  margin: 0 35%;
  padding: 5px;
  font-size: 20px;
  outline: 3px solid red;
  text-align: center;
  z-index: 999;
}