how professionals make website element's size fit to window size and zoom changing,or how they know which real screen resolution is (before zooming).
let me assume that i put a background to full window only if the browser window is full screen and if the browser window size has changed to 80px in width and height then it must appear only the bit of background that must be shown in the standard way.
i mean that if the user open my website and his window was not full how to show only the bit of background that must appear.
thanks a lot.
Look into the bootstrap framework: http://getbootstrap.com/css/#grid-intro
The grid system is probably what you were looking for.
Hope this helps.