css获得屏幕分辨率的高度

im having a hard time getting the height of lower screen resolution because my screen resolution is 1920x1080 does anyone know how to get the height and width screen resolution? because my friend has 1024x768 resolution when he checked my work into his computer, its all messed up, this is my only problem when it comes to CSS the height and width.im having a hard time getting the height of low