responsive sprites / percentages

Question

I\'ve read every single question about responsive sprites using css, I saw jsfiddle with working examples of responsive sprites, but I still cannot understand how to get the

Answer 1

The div dimension doesn't play in the calculus, only the background sizes, and the part that you are going to use.

Lets say that your background has a width of 1000px and a height of 500px.

The image that you are going to use has 80px width and height.

background-size:

x part     1000px / 80px = 12.5   ->> 1250%
y part      500px / 80px = 6.25   ->>  625%

background-size: 1250% 625%;

background-position:

x-part     173px / 1000px = 0.173   ->> 17.3%
y part     293px / 500px = 0.586    ->> 58.6%

background-position: 17.3% 58.6%;