In css file main (located in folder css) they used fixed heights for:
‘header’
‘site-title’
‘slider_container’
‘flexslider .slides li’
But also in mobile stylesheets in same file (displayed underneath Media Queries).
Fixed heights is not the best way to do this, especially not in mobile stylesheets. You should play with them.
Slider css for normal desktop pc is also located in css file flexslider (located in lib > flexslider)
Guido