How do I make an image relative to the screen size in css?

Question

I have an image background in css and 2 images overlaying that. On my device I can line them up perfectly the way I want, but when I go to view them on another device or change my screen size, the 2 overlaying images change size and position while the background doesn't. I know there's a line of css that I'm missing or doing wrong, so if anyone could help it would be much appreciated. Thanks, and here's my code:

Answer 1

实际上没关系，我刚刚发现通过使用百分比而不是像素来自动调整位置和宽度。