Here's a list of better units to use if you want it to look the same on all screens.
Honestly, I pretty much suck at CSS and I honestly don't understand how i'd use it, but what I can tell you is that I am using a 2017 iMac, so you should be able to tell the screen size based on that. I am also using Firefox on MacOS.
not sure if you can view this since it's blocked in some countries, but here's a catbox upload.
OMG Wow, it looks so damn good! I wish it worked for me!
right, I just noticed that, because I'm mixing percentages and absolute units here, the image actually moves around as I change the screen size. I'll refine the example with more reliability later today.
No worries or hurries, take your time on this and let me know :)