Creating a Fixed Width Button in CSS

I have several buttons with a variable width, and I would like all of them to be of a certain width. When I tried to add width: 150px;, this will not work. How to create these buttons that will have a given width?

Here is the fiddle and here is the code:

HTML

<p><a class="dark_button 150px-width" href="#">Lorem</a></p>
<p><a class="dark_button 150px-width" href="#">Lorum Ipsum</a></p>
<p><a class="dark_button 150px-width" href="#">Lorum Ipsum dolor</a></p>
<p><a class="dark_button 150px-width" href="#">Lorum Ipsum dolor sit amet</a></p>

CSS

.dark_button{
  border-top: 1px solid #969696;
  background: #000000;
  background: -webkit-gradient(linear, left top, left bottom, from(#545454), to(#000000));
  background: -webkit-linear-gradient(top, #545454, #000000);
  background: -moz-linear-gradient(top, #545454, #000000);
  background: -ms-linear-gradient(top, #545454, #000000);
  background: -o-linear-gradient(top, #545454, #000000);
  padding: 5px 10px;
  -webkit-border-radius: 8px;
  -moz-border-radius: 8px;
  border-radius: 8px;
  -webkit-box-shadow: rgba(0,0,0,1) 0 1px 0;
  -moz-box-shadow: rgba(0,0,0,1) 0 1px 0;
  box-shadow: rgba(0,0,0,1) 0 1px 0;
  text-shadow: rgba(0,0,0,.4) 0 1px 0;
  color: #e3e3e3 !important;
  font-size: 14px;
  text-decoration: none;
  vertical-align: middle;
}
.dark_button:hover {
  border-top-color: #4f4f4f;
  background: #4f4f4f;
  color: #ccc;
  text-decoration:none;
}
.dark_button:active {
  border-top-color: #4a4a4a;
  background: #4a4a4a;
}

.150px-width{
 width: 150px;
}