The imac is often used in webdesign. But if you want to integrate an HD image to the site, the weight of the image is very large and slows down the site.
We must therefore address this issue with CSS3 . Replace a picture of more than 100 kb in a CSS file of 2 kb.
This file is :
available in all sizes you need with the percentage. working with all modern Browsers. not using images. very simple to integrate. light.
Post-Scriptum
My speciality is to convert some image or psd to CSS , if you have a suggest let me a comment