CSS - Transform function not working on links?

Question

I did like so when a href's extension is .pdf; .doc; .ppt; .xls then it'll add corresponding file picture in front of it. Then I tried making a link go smaller when I hover over it but I doesn't do anything! Am I doing something wrong or what?

Code:

ul{
  list-style-type: none;
}
ul a{
  text-decoration:none;
  padding-left: 20px;
  background-repeat: no-repeat;
}
ul a:hover{
  text-decoration:underline;
  color:#666;
  -moz-transform: scale(0.9);
  -webkit-transform: scale(0.9);
  -ms-transform: scale(0.9);
  transform: scale(0.9);
}
a[href$=".pdf"]{
  background-image:url(http://i.stack.imgur.com/zJlYq.gif);
}
a[href$=".doc"]{
  background-image:url(http://i.stack.imgur.com/z2lbW.gif);
}
a[href$=".ppt"]{
  background-image:url(http://i.stack.imgur.com/Tk5Vv.gif);
}
a[href$=".xls"]{
  background-image:url(http://i.stack.imgur.com/sOr7E.gif);
}

<ul>
  <li><a href="/one.pdf">pdf</a></li>
  <li><a href="/two.doc">doc</a></li>
  <li><a href="/three.ppt">ppt</a></li>
  <li><a href="/four.xls">xls</a></li>
</ul>

Answer 1

You should use display: inline-block for <a> tag (or display: block), because <a> has display: inline by default, but transformable element can't be with display: inline:

Transformable element — an element whose layout is governed by the CSS box model which is either a block-level or atomic inline-level element, or ...

Inline-block — this value causes an element to generate an inline-level block container. The inside of an inline-block is formatted as a block box, and the element itself is formatted as an atomic inline-level box.

ul {
    list-style-type: none;
}

ul a {
    text-decoration: none;
    padding-left: 20px;
    background-repeat: no-repeat;
    display: inline-block;
}

ul a:hover {
    text-decoration: underline;
    color: #666;
    -webkit-transform: scale(0.9);
    -moz-transform: scale(0.9);
    -ms-transform: scale(0.9);
    transform: scale(0.9);
}

a[href $= '.pdf'] {
    background-image: url(http://i.stack.imgur.com/zJlYq.gif);
}

a[href $= '.doc'] {
    background-image: url(http://i.stack.imgur.com/z2lbW.gif);
}

a[href $= '.ppt'] {
    background-image: url(http://i.stack.imgur.com/Tk5Vv.gif);
}

a[href $= '.xls'] {
    background-image: url(http://i.stack.imgur.com/sOr7E.gif);
}

<ul>
    <li><a href="/one.pdf">pdf</a></li>
    <li><a href="/two.doc">doc</a></li>
    <li><a href="/three.ppt">ppt</a></li>
    <li><a href="/four.xls">xls</a></li>
</ul>