Fleche prev et next manquant sur le slide

Bonjour,
J'ai ajouter un slide sur le site, et les boutons next et prev sont manquant malgré ce code css:

#prevBtn, #nextBtn, #sliderprev, #slidernext{
margin:0;
padding:0;
display:block;
overflow:hidden;
text-indent:-8000px;
}
/* // image replacement */

/* Easy Slider */
#slider ul, #slider li{
margin:0;
padding:0;
list-style:none;
}
#slider li {
width:930px;
height:322px;
overflow:hidden;
}
#slider li a {
display:block;
width:930px;
height:40px;
margin-top:282px;
padding:10px;
text-align:left;
color:#fff;
font-size:20px;
text-decoration:none;
background:url("../images/transparent_bg.png") repeat;
}

* html #slider li a {
background-image:none;
background:#000000;
filter : alpha(opacity=60); /* IE < 8 */
}

li#img_1{
background:url(../images/01.jpg) no-repeat 0 0;
}
li#img_2{
background:url(../images/02.jpg) no-repeat 0 0;
}
li#img_3{
background:url(../images/03.jpg) no-repeat 0 0;
}
li#img_4{
background:url(../images/04.jpg) no-repeat 0 0;
}
#prevBtn, #nextBtn{
}
#slidernext, #sliderprev{
display:block;
width:30px;
height:77px;
position:absolute;
left:-30px;
top:71px;
z-index:1000;
}
#nextBtn, #slidernext{
left:696px;
}
#prevBtn a, #nextBtn a{
background:url(../images/btn_prev.gif) no-repeat 0 0;
}
#slidernext a, #sliderprev a{
display:block;
position:relative;
width:30px;
height:77px;
}
#nextBtn a, #slidernext a{
background:url(../images/btn_next.gif) no-repeat 0 0;
}

/* numeric controls */

ol#controls{
margin:1em 0;
margin-top:-32px;
margin-left:770px;
padding:0;
height:28px;
}
ol#controls li{
margin:0 10px 0 0;
padding:0;
float:left;
list-style:none;
height:28px;
line-height:28px;
}
ol#controls li a{
float:left;
height:28px;
line-height:28px;
border:1px solid #ccc;
background:#DAF3F8;
color:#555;
padding:0 10px;
text-decoration:none;
}
ol#controls li.current a{
background:orangered;
color:#fff;
}
ol#controls li a:focus, #prevBtn a:focus, #nextBtn a:focus{outline:none;}
/* // Easy Slider */