My navigation buttons are first joined and just then split to some extent..

Hi every one!!!
I have a problem that is

My website navigation bar is of 5 buttons situated apart from them.
but when i go to site...these button first seems to be joined and after some while they get apart.

My css for menu buttons is>>

/* begin Menu */
/* menu structure */

.art-menu a, .art-menu a:link, .art-menu a:visited, .art-menu a:hover
{
text-align:left;
text-decoration:none;
outline:none;
letter-spacing:normal;
word-spacing:normal;
}

.art-menu, .art-menu ul
{
margin: 30px;
margin-top:0px;
margin-bottom:0px;

padding: 0px;
border: 0px;
list-style-type: none;
display: block;
}

.art-menu li
{
margin: 0px;
padding: 0;
border: 0;
display: block;
float: left;
position: relative;
z-index: 5;
background:none;
}

.art-menu li:hover
{
z-index: 10000;
white-space: normal;
}

.art-menu li li
{
float: none;
}

.art-menu ul
{
visibility: hidden;
position: absolute;
z-index: 10;
left: 0;
top: 0;
background:none;
}

.art-menu li:hover>ul
{
visibility: visible;
top: 100%;
}

.art-menu li li:hover>ul
{
top: 0;
left: 100%;
}

.art-menu:after, .art-menu ul:after
{
content: ".";
height: 0;
display: block;
visibility: hidden;
overflow: hidden;
clear: both;
}
.art-menu, .art-menu ul
{
min-height: 0px;
top:0px;
}

.art-menu ul
{

padding: 10px 30px 30px 30px;
margin: -2px 0 0 -6px;
}

.art-menu ul ul
{
padding: 30px 30px 30px 10px;
margin: -30px 0 0 -10px;
}





/* menu structure */

.art-menu
{
padding: 20px 20px 20px 20px;
}

.art-nav
{
position: relative;
height: 40px;
z-index: 100;
top:0px;

}


/* end Menu */

/* begin MenuItem */
.art-menu ul li
{
clear: both;
}

.art-menu a
{
position:relative;
display: block;
overflow:hidden;
height: 28px;
cursor: pointer;
text-decoration: none;
margin-right: 1px;
margin-left: 1px;
}


.art-menu a .r, .art-menu a .l
{
position:absolute;
display: block;
top:0;
z-index:-1;
height: 84px;
background-image: url('images/MenuItem.png');
}

.art-menu a .l
{
left:0;
right:12px;
}

.art-menu a .r
{
width:424px;
right:0;
clip: rect(auto, auto, auto, 412px);
}

.art-menu a .t
{
font-family: Tahoma, Arial, Helvetica, Sans-Serif;
font-size: 13px;
color: #000000;
padding: 0 11px;
margin: 0 12px;
line-height: 28px;
text-align: center;
}

.art-menu a:hover .l, .art-menu a:hover .r
{
top:-28px;
}

.art-menu li:hover>a .l, .art-menu li:hover>a .r
{
top:-28px;
}

.art-menu li:hover a .l, .art-menu li:hover a .r
{
top:-28px;
}
.art-menu a:hover .t
{
color: #000000;
}

.art-menu li:hover a .t
{
color: #000000;
}

.art-menu li:hover>a .t
{
color: #000000;
}


.art-menu a.active .l, .art-menu a.active .r
{
top: -56px;
}

.art-menu a.active .t
{
color: #000000;
}


/* end MenuItem */



where is the mistake??

thanks in advance...

 

A link to the site would be helpful in pinpointing the problem.