How to build a form with multiple columns having different column width

Hi,

I have a simpleform in a panel and this simple form will have 3 columns. I am able to achieve this but the width of the columns is equally shared (form's width/3). However, I want to control the width of each columns. Lets say first column should have 20% width and rest two columns should have 40% each.

Is this possible with simple form ? If not, please advice me the best option.