Edit in JSFiddle

<!DOCTYPE html>
<html>

  <body>
    <section>
      <h1>XYN</h1></section>
    <header>

      <nav>
        <ul>
          <li>
            <h6>Gamefolio</h6>
            <a href="#">
              <div id="platform1"></div>
            </a>Games</li>
          <li>
            <h6>3Dfolio</h6>
            <a href="#">
              <div id="platform2"></div>
            </a>3D Modeling</li>
          <li>
            <h6>Graphicfolio</h6>
            <a href="#">
              <div id="platform3"></div>
            </a>Motion Graphics</li>
          <li>
            <h6>Webfolio</h6>
            <a href="#">
              <div id="platform4"></div>
            </a>Websites</li>
          <li>
            <h6>Conceptfolio</h6>
            <a href="#">
              <div id="platform5"></div>
            </a>Sketches</li>
        </ul>
      </nav>

    </header>
    <section></section>

  </body>

</html>
body {
  font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
  transition: all ease-in-out 0.2s;
  padding: 0px;
  margin: 0px;
  background: #FBFBFB;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-variant: small-caps;
  padding: 0px;
  margin: 0px;
}

h6 {
  font-size: 2em;
}

section {
  height: auto;
  width: 100%;
  color: #393939;
  text-align: center;
  font-size: 450%;
  font-family: Impact;
}

header {
  background: rgb(51, 51, 51);
  background: -moz-linear-gradient(top, rgba(51, 51, 51, 1) 1%, rgba(200, 200, 200, 0.25) 50%, rgba(51, 51, 51, 1) 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(1%, rgba(51, 51, 51, 1)), color-stop(50%, rgba(200, 200, 200, 0.25)), color-stop(100%, rgba(51, 51, 51, 1)));
  background: -webkit-linear-gradient(top, rgba(51, 51, 51, 1) 1%, rgba(200, 200, 200, 0.25) 50%, rgba(51, 51, 51, 1) 100%);
  background: -o-linear-gradient(top, rgba(51, 51, 51, 1) 1%, rgba(200, 200, 200, 0.25) 50%, rgba(51, 51, 51, 1) 100%);
  background: -ms-linear-gradient(top, rgba(51, 51, 51, 1) 1%, rgba(200, 200, 200, 0.25) 50%, rgba(51, 51, 51, 1) 100%);
  background: linear-gradient(to bottom, rgba(51, 51, 51, 1) 1%, rgba(200, 200, 200, 0.25) 50%, rgba(51, 51, 51, 1) 100%);
  filter: progid: DXImageTransform.Microsoft.gradient( startColorstr='#333333', endColorstr='#333333', GradientType=0);
  border-top: #ffffff solid 1px;
  border-bottom: #ffffff solid 1px;
  padding: 0px;
  margin: 0px;
  width: auto;
  height: 300px;
}

nav {
  width: 100%;
  height: auto;
  padding: 0px;
  margin: 0px 0px 0px 10%;
}

ul {
  width: 100%;
  height: 100%;
  padding: 0px;
  margin: 0px;
}

li {
  font-family: Impact;
  color: #efefef;
  text-decoration: none;
  font-size: 1em;
  text-align: center;
  margin: 25px -2% 50px -2%;
  padding: 0px;
  display: inline-block;
  height: 200px;
  width: 20%;
}

a {
  padding: 0px;
  margin: 0px;
  height: auto;
  width: auto;
}

nav ul li a div {
  -webkit-box-shadow: 0px 0px 25px 0px rgba(1, 1, 1, 0.75);
  box-shadow: 0px 0px 25px 0px rgba(1, 1, 1, 0.75);
  border: #efefef solid 0px;
  border-radius: 20px;
}

nav ul li a div:hover {
  -webkit-box-shadow: 0px 0px 25px 0px rgba(4, 4, 4, 0.5);
  box-shadow: 0px 0px 25px 0px rgba(4, 4, 4, 0.5);
  border: #efefef solid 0px;
  border-radius: 30px;
}

#platform1 {
  transition: all ease-in-out 0.2s;
  position: relative;
  z-index: 1;
  margin: 0px;
  padding: 0px;
  width: 100%;
  height: 200px;
  background: url(1.png) no-repeat center;
}

#platform1:hover {
  transition: all ease-in-out 0.2s;
  z-index: 4;
  padding: 5px;
  margin: -5px 75% -10px 0%;
  width: 175%;
  height: 200px;
  background: url(11.png) no-repeat center rgba(4, 4, 4, 1);
}

#platform2 {
  transition: all ease-in-out 0.2s;
  position: relative;
  z-index: 2;
  margin: 5px 0px 0px 0px;
  padding: 0px;
  width: 100%;
  height: 200px;
  background: url(2.png) no-repeat center;
}

#platform2:hover {
  padding: 5px;
  transition: all ease-in-out 0.2s;
  z-index: 4;
  margin: 0px -0% -10px -37.5%;
  width: 175%;
  height: 200px;
  background: url(21.png) no-repeat center rgba(4, 4, 4, 1);
}

#platform3 {
  transition: all ease-in-out 0.2s;
  position: relative;
  z-index: 3;
  margin: 10px 0px 0px 0px;
  padding: 0px;
  width: 100%;
  height: 200px;
  background: url(3.png) no-repeat center;
}

#platform3:hover {
  padding: 5px;
  transition: all ease-in-out 0.2s;
  z-index: 4;
  margin: 5px -0% -10px -37.5%;
  width: 175%;
  height: 200px;
  background: url(31.png) no-repeat center rgba(4, 4, 4, 1);
}

#platform4 {
  transition: all ease-in-out 0.2s;
  position: relative;
  z-index: 2;
  margin: 5px 0px 0px 0px;
  padding: 0px;
  width: 100%;
  height: 200px;
  background: url(4.png) no-repeat center;
}

#platform4:hover {
  padding: 5px;
  transition: all ease-in-out 0.2s;
  z-index: 4;
  margin: 0px -0% -10px -37.5%;
  width: 175%;
  height: 200px;
  background: url(41.png) no-repeat center rgba(4, 4, 4, 1);
}

#platform5 {
  transition: all ease-in-out 0.2s;
  position: relative;
  z-index: 1;
  margin: 0px;
  padding: 0px;
  width: 100%;
  height: 200px;
  background: url(5.png) no-repeat center;
}

#platform5:hover {
  padding: 5px;
  transition: all ease-in-out 0.2s;
  z-index: 4;
  margin: -5px -0% -10px -75%;
  width: 175%;
  height: 200px;
  background: url(51.png) no-repeat center rgba(4, 4, 4, 1);
}