Today, I've found that we can adjust background image with percentage in CSS. The time before I knew only to adjust background image with two positions. It's left, right, center and bottom, up position. Now I know is to adjust by percentage for those two positions.
background: url("img") no-repeat center left;
Here is modern adjustment
background: url("img") no-repeat 50% 25%;
It's cool, isn't it?