nav {  
   display: block;  
   width: 100%;  
   overflow: hidden;  
  }  

  nav ul {  
   margin: 80px 0 20px 0;  
   padding: .7em;  
   float: left;  
   list-style: none;  
   background: #444;  
   background: rgba(0,0,0,.2);  
   -moz-border-radius: .5em;  
   -webkit-border-radius: .5em;  
   border-radius: .5em;   
   -moz-box-shadow: 0 1px 0 rgba(255,255,255,.2), 0 2px 1px rgba(0,0,0,.8) inset;  
   -webkit-box-shadow: 0 1px 0 rgba(255,255,255,.2), 0 2px 1px rgba(0,0,0,.8) inset;  
   box-shadow: 0 1px 0 rgba(255,255,255,.2), 0 2px 1px rgba(0,0,0,.8) inset;   
  }  

  nav li {  
   float:left;  
  }  

  nav a {  
   float:left;  
   padding: .8em 1.5em;  
   text-decoration: none;  
   color: #555;  
   text-shadow: 0 1px 0 rgba(255,255,255,.5);  
   font: bold 1.1em/1 'trebuchet MS', Arial, Helvetica;  
   letter-spacing: 1px;  
   text-transform: uppercase;  
   border-width: 1px;  
   border-style: solid;  
   border-color: #fff #ccc #999 #eee;  
   background: #c1c1c1;  
   background: -moz-linear-gradient(#f5f5f5, #c1c1c1);  
   background: -webkit-gradient(linear, left top, left bottom, from(#f5f5f5), to(#c1c1c1));  
   background: -webkit-linear-gradient(#f5f5f5, #c1c1c1);  
   background: -o-linear-gradient(#f5f5f5, #c1c1c1);  
   background: -ms-linear-gradient(#f5f5f5, #c1c1c1);  
   background: linear-gradient(#f5f5f5, #c1c1c1);   
   }  
     
  nav a:hover, nav a:focus {  
   outline: 0;  
   color: #fff;  
   text-shadow: 0 1px 0 rgba(0,0,0,.2);  
   background: #fac754;  
   background: -moz-linear-gradient(#fac754, #f8ac00);  
   background: -webkit-gradient(linear, left top, left bottom, from(#fac754), to(#f8ac00));  
   background: -webkit-linear-gradient(#fac754, #f8ac00);  
   background: -o-linear-gradient(#fac754, #f8ac00);  
   background: -ms-linear-gradient(#fac754, #f8ac00);  
   background: linear-gradient(#fac754, #f8ac00);  
  }  

  nav a:active {  
   -moz-box-shadow: 0 0 2px 2px rgba(0,0,0,.3) inset;  
   -webkit-box-shadow: 0 0 2px 2px rgba(0,0,0,.3) inset;  
   box-shadow: 0 0 2px 2px rgba(0,0,0,.3) inset;  
  }  
     
  nav li:first-child a {  
   border-left: 0;  
   -moz-border-radius: 4px 0 0 4px;  
   -webkit-border-radius: 4px 0 0 4px;  
   border-radius: 4px 0 0 4px;   
  }  

  nav li:last-child a {  
   border-right: 0;  
   -moz-border-radius: 0 4px 4px 0;  
   -webkit-border-radius: 0 4px 4px 0;  
   border-radius: 0 4px 4px 0;   
  }

<nav>  
   <ul>  
   <li><a href="">Главная</a></li>  
   <li><a href="">Категории</a></li>  
   <li><a href="">О нас</a></li>   
   <li><a href="">Портфолио</a></li>  
   <li><a href="">Контакт</a></li>  
   </ul>  
  </nav>