How can I set the max-width of a table cell using percentages?

Old question I know, but this is now possible using the css property table-layout: fixed on the table tag. Answer below from this question CSS percentage width and text-overflow in a table cell

This is easily done by using table-layout: fixed, but a little tricky because not many people know about this CSS property.

table {
  width: 100%;
  table-layout: fixed;
}

See it in action at the updated fiddle here: http://jsfiddle.net/Fm5bM/4/

According to the definition of max-width in the CSS 2.1 spec, “the effect of 'min-width' and 'max-width' on tables, inline tables, table cells, table columns, and column groups is undefined.” So you cannot directly set max-width on a td element.

If you just want the second column to take up at most 67%, then you can set the width (which is in effect minimum width, for table cells) to 33%, e.g. in the example case

td:first-child { width: 33% ;}

Setting that for both columns won’t work that well, since it tends to make browsers give the columns equal width.