Can you try the below code, wrapping those span within a class. Check this JSFiddle
.list-a .desc-fix {
width: 100%;
height: 100%;
}
.list-a .desc {
background: url("../images/trans_black.png") repeat;
display: block;
font-family: arial;
font-size: small;
margin: 3px 0 0 50px;
padding: 10px;
max-width:300px;
max-heigtht: 400px;
width: 100%;
height: 100%;
}
.list-a {
width:300px;
height:400px;
margin: 0px auto;
}