How can I make a link inside a div fill the entire space inside the div?

I have a div that has a set width and it is wrapped around a link. I want the link inside to fill the entire space of the div so that when I click anywhere inside the div (which I have styled to look like a button) it goes to the link. This is what I have tried, but .link_class doesn't do what I want. Any suggestions?

HTML:

<div class="button_class">
    <a class="link_class" href="http://www.my_link.com>My Link</a>
</div>

CSS:

.button_class {
    width:150px;
    padding:5px 7px;
    color:#fff;
    text-align:center;
    -webkit-border-radius:3px;
    -moz-border-radius:3px;
    border-radius:3px;
}

.link_class {
    width:100%;
    height:100%;
}

This should do the trick:-

By default a is an inline element and width does not affect them. So change it to inline-block to have it take the width you specify.

.link_class {
    display:inline-block;
    width:100%;
    height:100%;
}

Fiddle

Here is the Solution.

The HTML:

<div class="button_class">
    <a class="link_class" href="http://www.my_link.com">My Link</a>
</div>

The CSS:

.button_class {
    width:150px;
    color:#fff;
    text-align:center;
    -webkit-border-radius:3px;
    -moz-border-radius:3px;
    border-radius:3px;
    background:blue;
}

.link_class {
    display:block;
    color:#ffffff;
    overflow:auto;
    padding:5px 7px;    
}

Hope this helps.

I know this is an old question, but HTML5 has a better way to do this.

The answer today is:

HTML:

<a class="link_class" href="http://www.my_link.com>
   <div class="button_class">My Link</div>
</a>

CSS stays the same, except you don't need .link_class anymore.

This worked. The key was to explicitly set the div height and then use line-height on the link.

.button_class {
    width:150px;
    height:30px;
    color:#fff;
    text-align:center;
    -webkit-border-radius:3px;
    -moz-border-radius:3px;
    border-radius:3px;
}

.link_class {
    display:inline-block;
    width:100%;
    line-height:30px;
}

You need to make the link a block level element.

.link_class {
    display: block;
}