I need to to format or design my webpage using CSS. I want to have a body size of the page just large enough to accomodate all screen sizes. Then inside the body I need to have few boxes/columns inside the webpage there is basically going to be 3 columns 40%, 20% & 30 % and the rest used up by padding etc. All this will be done using css div.largecolumn, div.small column etc.

What I dont know how to do is to fomat the whole body to a size that I want and then after I aslo need to format the div tags to be able to fit into the new body size. Will I be able to format the div tags in css directly eg. div.largecolumn {width: 40%} also will I be able to use percentage rather than px because I have no clue how to measure a page using pixels or will I need to reference them after body tag?