HTML colspan in CSS

There is no colspan in css as far as I know, but there will be column-span for multi column layout in the near future, but since it is only a draft in CSS3, you can check it in here. Anyway you can do a workaround using div and span with table-like display like this.

This would be the HTML:

<div class="table">
  <div class="row">
    <span class="cell red first"></span>
    <span class="cell blue fill"></span>
    <span class="cell green last"></span>
  </div>
</div>
<div class="table">
  <div class="row">
    <span class="cell black"></span>
  </div>
</div>

And this would be the css:

  /* this is to reproduce table-like structure
     for the sake of table-less layout. */
  .table { display:table; table-layout:fixed; width:100px; }
  .row { display:table-row; height:10px; }
  .cell { display:table-cell; }

  /* this is where the colspan tricks works. */
  span { width:100%; }

  /* below is for visual recognition test purposes only. */
  .red { background:red; }
  .blue { background:blue; }
  .green { background:green; }
  .black { background:black; }

  /* this is the benefit of using table display, it is able 
     to set the width of it's child object to fill the rest of 
     the parent width as in table */
  .first { width: 20px; }
  .last { width: 30px; }
  .fill { width: 100%; }

The only reason to use this trick is to gain the benefit of table-layout behaviour, I use it alot if only setting div and span width to certain percentage didn't fullfil our design requirement.

But if you don't need to benefit from the table-layout behaviour, then durilai's answer would suit you enough.

<div style="width: 100%;">
    <div style="float: left; width: 33%;">Row 1 - Cell 1</div>
    <div style="float: left; width: 34%;">Row 1 - Cell 2</div>
    <div style="float: left; width: 33%;">Row 1 - Cell 3</div>
</div>
<div style="clear: left; width: 100%;">
Row 2 - Cell 1
</div>

Another suggestion is using flexbox instead of tables altogether. This is a "modern browser" thing of course, but come on, it's 2016 ;)

At least this might be an alternative solution for those looking for an answer to this nowadays, since the original post was from 2010.

Here's a great guide: https://css-tricks.com/snippets/css/a-guide-to-flexbox/

.table {
  border: 1px solid red;
  padding: 2px;
  max-width: 300px;
  display: flex;
  flex-flow: row wrap;
}
.table-cell {
  border: 1px solid blue;
  flex: 1 30%;
}
.colspan-3 {
  border: 1px solid green;
  flex: 1 100%;
}

<div class="table">
  <div class="table-cell">
    row 1 - cell 1
  </div>
  <div class="table-cell">
    row 1 - cell 2
  </div>
  <div class="table-cell">
    row 1 - cell 3
  </div>
  <div class="table-cell colspan-3">
    row 2 - cell 1 (spans 3 columns)
  </div>
</div>

There's no simple, elegant CSS analog for colspan.

Searches on this very issue will return a variety of solutions that include a bevy of alternatives, including absolute positioning, sizing, along with a similar variety of browser- and circumstance-specific caveats. Read, and make the best informed decision you can based on what you find.