I thought I would share some interesting information.
So the pixel ratio is the ratio between the actual device pixels vs dense pixels. I think vw units took the place of dp units. Not sure.
Pixels will look the same across different devices because of the math from the device behind the scenes. If we want to change that we use vw and em units. So it’s not the actual pixels on your device unless it’s the base at 160 dpi. 1 pixel = 160 dpi and 2 pixels = 320 dpi and so on.
Here’s an 8-year-old video that I found very helpful. It’s the only video I could find on the subject. 
