<div style="height:100%;"><div>.</div></div>
Although, you may wish to modify this to even 105%.
So set, it will correspond to the user's browser when created.
I've not found it that satisfactory, but you may wish to also set the size of controls (and other elements) by %, as well, to maintain proportionality.
Now - on the other hand - if you wish to really modify the window continuously: you can use the DOM (javaScript) and modify this property when the window height is modified. This is probably not worth your trouble.