How do I control the column width when exporting a table to HTML?

I know how to control the width of the table, but not the width of its columns. For example, I want the width of column A to be 2 cm and the width of B to be 4 cm:

|  A |  B |
|----+----|
| 11 | 12 |
| 21 | 22 |

Relative settings are also appreciated, A 33% and B 67% of total table width.

Thanks for reading, Martin