How to apply style classes to td classes?

Give the table a class name and then you target the td's with the following:

table.classname td {
    font-size: 90%;
}

If I remember well, some CSS properties you apply to table are not inherited as expected. So you should indeed apply the style directly to td,tr and th elements.

If you need to add styling to each column, use the <col> element in your table.

See an example here: http://jsfiddle.net/GlauberRocha/xkuRA/2/

NB: You can't have a margin in a td. Use padding instead.

You can use :nth-child(N) CSS selector like :

table td:first-child {}  //1
table td:nth-child(2) {} //2
table td:nth-child(3) {} //3
table td:last-child {}   //4