Small question. I'm trying out responsive design to create a site that will work on desktops but also potentially phones and such. The basic parts of this design seem to make sense but Im not clear on height. Like I have a logo at the top and then below that is a menu bar. I can't think how to set the height between those as a percentage because the height of the page will vary based on content and so at least to my understanding it seems like it would become potentially stretched vertically.

Height wise if i want it to be fairly specific should I just be specifying EM?

Thanks for reading.