I need to align 2 divs side by side. They are both inside of a wrapper div that has no set height.

My problem is when I use float:left and float:right respectively, the div's don't appear to "stay inside" the wrapper div (I can tell as the wrapper div has a different background colour to the page and this isn't being extended to cover the 2 divs I want to position). 

Basically I need the 2 div's to be side by side, but WITHIN this wrapper.

Apologies for the [very poor] attempt at describing this problem, I don't do much design work.