Give redirect warning close button more area to make it easier to touch on mobile

[ShirleyNekoDev]

I made the close button for the redirect warning a separate CSS "layer" (not really, but you'll see what I mean) and added a padding around the X so that you can hit it easier on mobile.

I also added a localStorage banner suppression which saves the hidden state of the banner (aside from using the redirect.io session stuff). * As this has already been fixed minutes before I commited my changes, I can remove that part if you want to. ;)

I hope this helps.

Screenshots for different sizes below (outline around button to represent click area, not visible in PR code) :

Btw. this banner close button differs from the unicode "×" used in the mobile app banner below 🤔