CSS: Make a block element fill the entire space of a parent element?

Question

I am trying to put a link in a element and have the element fill the entire space of the . While I can

Answer 1

The closest i got was this...

th {
  float: left;
  overflow: hidden;
  font-size: 50%;
  width: 20em;
  margin: auto;
}
th a {
  display: table; /* or block, up to you */
  margin: none;
  width:100%;
  height: 1px;
  background-color: #aaa;
  padding: 20%;
}

But it makes all your rows the same height. Maybe someone else can fix that if it's a problem.