Fit code/website on all screens (devices)

Question

Anybody know about @media (CSS) - it's to fit your website on all different kind of screens.
For example, let's say I'm trying to make the .content width decrease every time the body width decreases.,
Like this -
(max width (300px) = .content width = 300px;
(max width 299px) = .content width = 299px
(max width 298px) - = .content width = 298px)...

So my point is instead of typing every number, could I use JavaScript to make the .content width decrease evytime the body decreases?
Something like i - - or (i ++).
Let me know if it doesn't make sense

Answer 1

I suggest you give Gordon 's
https://code.sololearn.com/W3gS00IGw160/?ref=app a lookover.