Use relative width and height for all elements

Hi!

The main container's width is set to 1024px, causing it to get too small on bigger displays (unzoom to test):

Having the orange bars at the left and right of the main container taking more than 50% of the available space is probably unwanted.

Using relative width and font size (in % or vh/vw) would help a lot.

Suggestion: use 100vh for the first pane (main container) and 100vh for the secondary pane (main footer).

Those orange bars really fits PeerTube's style, even though I feel like it gives a kind of oldish style to the page (no offense! 😅 ). Setting relative width on the main container size would imply that we need to agree on the size (in % ?) of those bars, that currently fully depends on the user's screen resolution. What about 85% for the main container, so 7.5/7.5 % for both orange bars?

Here's the main container resized at 85% instead of 1024px:

As said above, also setting relative font sizes would be necessary for bigger displays.

If you folks are okay about those edits, I can work on a PR to address this issue.

Thanks for reading!

~ Neil for 42l