Unable to change li Background Color on Hover

Unable to change li Background Color on Hover

Can you please take a look at this link and let me know why I am not able
to change the background color of the li on hover?
<ul class="inline">
<li>1</li>
<li>2</li>
<li>3</li>
<li>3</li>
<li>3</li>
</ul>
Css:
.inline li{
width:18% !important;
background:#FFF !important;
}
.inline li: hover{
background:#A5A5A5 !important;
}