Use of Navigation Bar in CSS

hello friend,
this is example code...

nav-example {
background:url("https://lh4.googleusercontent.com/-xbhbCcnBhYI/Tft-OgZOwTI/AAAAAAAABII/lh1EAkmm0ps/s800/final-nav-bar.png") no-repeat;
width:495px;
height:48px;
margin:0;
padding:0;
}
#nav-example span {
display: none;
}
#nav-example li, #nav-example a {
height:48px;
display:block;
}
#nav-example li {
float:left;
list-style:none;
display:inline;
}
#nav-example-1 {width: 125px;}
#nav-example-2 {width: 122px;}
#nav-example-3 {width: 122px;}
#nav-example-4 {width: 123px;}
#nav-example-1 a:hover {background:url("https://lh4.googleusercontent.com/-xbhbCcnBhYI/Tft-OgZOwTI/AAAAAAAABII/lh1EAkmm0ps/s800/final-nav-bar.png") 0px -48px no-repeat; }
#nav-example-2 a:hover {background:url("https://lh4.googleusercontent.com/-xbhbCcnBhYI/Tft-OgZOwTI/AAAAAAAABII/lh1EAkmm0ps/s800/final-nav-bar.png") -125px -48px no-repeat; }
#nav-example-3 a:hover {background:url("https://lh4.googleusercontent.com/-xbhbCcnBhYI/Tft-OgZOwTI/AAAAAAAABII/lh1EAkmm0ps/s800/final-nav-bar.png") -247px -48px no-repeat; }
#nav-example-4 a:hover {background:url("https://lh4.googleusercontent.com/-xbhbCcnBhYI/Tft-OgZOwTI/AAAAAAAABII/lh1EAkmm0ps/s800/final-nav-bar.png") -369px -48px no-repeat; }

regards,