Borderless UI follow up fixes

[jaril]

Fix #4309.

1. 8px vertical border between the video and the sidepanels
   
2. Made the share button height ~32px. This isn't quite the same as 34px as the view toggle, but because of the gray border the view toggle looks a tad smaller than it actually does and this ends up looking 👌. Thoughts welcome.
   
3. Can't reproduce this one.
4. Made the padding around the toolbar 8px.
   
5. Made an executive decision on the border underneath the header and made it thinner so it's more consistent with the other gaps. Otherwise it ended up looking too thick.
   

@jonbell-lot23 I'll leave the decision re: #2 and #5 to you. Let me know what you think!

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[jonbell-lot23]

Love 'em, thanks!

[jasonLaster]

I spy a border 😉

[jasonLaster]

Looking great! Love these tweaks