Browsing nav cleanup (#21418)

* tweak hover style

* SidebarSection and padding adjustments

* color tweaks

* tweak alignment

* tweak icons + positioning

* fix browse spacing

* Fix prop type

* Wrap bookmarks list with `ul`

* Fix using `li` while not being in a list

* Keep collection's section "more" icon visible

* Migrate to emotion

* Make "more" icon container an HTML button

* TippyPopoverWithTrigger

* Fix e2e helpers to toggle nav sidebar

* Fix closing sidebar on collection tag on mobile

* Fix settings icon background hover color

* Fix sidebar width responsiveness

* Fix settings icon position

* Fix e2e tests

* Fix icon sizes

* Fix CollapseSection style

* Revert Tree changes

* Get sidebar style back

* Fix bookmarked question color

* Fix Tree padding

* Remove redundant constant

* Fix color

* Fix e2e tests

Co-authored-by: Anton Kulyk <kuliks.anton@gmail.com>