Using CSS, how to create a two-column grid with equal-width columns that are “only as narrow as required”?

Answer 1

Just revisited this now since CSS Grid has become much more supported. One solution for CSS Grid would be this:

.linkgrid {
  display: inline-grid;
  grid-template-columns: repeat(2, 1fr);
  column-gap: 10px;
  row-gap: 10px;
}

.gridentry > * {
  display: block;

  padding: 10px;

  text-align: center;
  
  background-color: red;
  color: white;

  /* This is helpful if the texts get too long to break them "naturally": */
  /* word-break: break-all; */
}

<div class="linkgrid">
  <div class="gridentry">
    <a href="#">Loooooooooooooong</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
  <div class="gridentry">
    <a href="#">Meeeedium</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
</div>

Answer 2

After fiddling around with this for quite a while and getting a very helpful answer to another question that was related to this one, I managed to finally find a solution:

.linkgrid {
  max-width: 50%;
  display: table;
}

.gridentry:nth-child(odd) {
  float: left;
  width: 100%;
}

.gridentry:nth-child(even) {
  width: 100%;
  margin-left: 100%;
  margin-right: -100%;
}

.gridentry:nth-child(even):after {
  content: '';
  display: block;
  clear: left;
}

.gridentry > * {
  display: block;
  
  margin-bottom: 10px;
  padding: 10px;

  background-color: red;
  text-align: center;

  /* This is helpful if the texts get too long to break them "naturally": */
  /* word-break: break-all; */
}

.gridentry:nth-child(odd) > * {
  margin-right: 5px;
}

.gridentry:nth-child(even) > * {
  margin-left: 5px;
}

.gridentry a {
  color: white;
}

<div class="linkgrid">
  <div class="gridentry">
    <a href="#">Loooooooooooooong</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
  <div class="gridentry">
    <a href="#">Meeeedium</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
  <div class="gridentry">
    <a href="#">Short</a>
  </div>
</div>