Responsive image slider height

Hi, id like to have image slider only to certain point of the page. Ive added such code into the Custom CSS filed in Theme Options: [code] #feature-slider .slides { width: 100%; height: 75%; } #feature-slider .entry-container { display: none; } [/code] But it turns off the slider completely. When i replace "75%" with something like "500px" it works perfect. But i`d much more like to have the image covering like 75% of the screen, regardless of the screen resolution.