How to achieve the same responsiveness of div blocks as with the "background-size: cover;" property for img?

Question

Adaptive design

when changing the screen resolution, blocks with the specified height and width in% slowly change their size relative to the center. How to make the blocks in relation to the center remain unchanged, but somehow go beyond the screen (in case of zooming out, for example)?
or so that the entire site is scaled as with the background-size: cover property; for img?
And another question) why do the colors that you take from Photoshop change hue when applied in the code?
thank!

Answer 1

try bacground-size: 100%
because it should be in RGB(255,255,255)

Answer 2

Or use a wrapper or throw a picture as a background.