Site ser godt ud i Firefox, men grimt i andre browsere. What to do?

CSS kode 

 #bord {
  position: relative;
 }
 
 #telefon {
  position: absolute;
  top: 100px;
  left: 200px;
  width: 200px;
 }

HTML kode 

 <div id="iphone5">
 <a href="communication.html" title="Kommunikation"><img src="images/hover-btn.png" /></a>
 </div> <!-- end #iphone5 -->
 
 <div id="tools">
 <a href="interaction.html" title="Interaktion"><img src="images/hover-btn.png" /></a>
 </div> <!-- end #tools -->
 
 <div id="paperwork">
 <a href="business.html" title="Virksomhed"><img src="images/hover-btn.png" /></a>
 </div> <!-- end #paperwork -->
 
 <div id="sketchbook">
 <a href="visualisation.html" title="Visualisering"><img src="images/hover-btn.png" /></a>
 </div> <!-- end #sketchbook -->

CSS kode 

 #iphone5 {
     float:right;
     margin-right:14%;
     margin-top:17%;
     background:url(images/iphone5.png);
     background-repeat:no-repeat;
     background-size:contain;
     width:5%;
     height:10%;
 }
 
 #iphone5:hover {
     border:solid transparent;
 }
 
 #iphone5 img {
     width:100%;
     height:100%;
 }
 
 #tools {
     float:left;
     margin-left:17%;
     margin-top:3%;
     background:url(images/tools.png);
     background-repeat:no-repeat;
     background-size:contain;
     width:15%;
     height:25%;
 }
 
 #tools:hover {
     border:solid transparent;
 }
 
 #tools img {
     width:100%;
     height:100%;
 }
 
 #paperwork {
     float:left;
     margin-left:6%;
     margin-top:-1%;
     background:url(images/paperwork.png);
     background-repeat:no-repeat;
     background-size:contain;
     width:17%;
     height:20%;
 }
 
 #paperwork:hover {
     border:solid transparent;
 }
 
 #paperwork img {
     width:100%;
     height:100%;
 }
 
 #sketchbook {
     float:left;
     margin-left:10%;
     margin-top:-8%;
     background:url(images/sketchbook.png);
     background-repeat:no-repeat;
     background-size:contain;
     width:13%;
     height:30%;
 }
 
 #sketchbook:hover {
     border:solid transparent;
 }
 
 #sketchbook img {
     width:100%;
     height:100%;
 }