css: Nest `.hotspot-popover` arrows inside `.hotspot.overlay`.
css: Nest `.hotspot-popover` arrows inside `.hotspot.overlay`.

No changes were required in night mode since the night-mode css
already includes the same level of nesting.
Tested visually as well.

kou/zulip,timabbott/zulip,eeshangarg/zulip,timabbott/zulip,rishig/zulip,rht/zulip,showell/zulip,andersk/zulip,brainwane/zulip,kou/zulip,rht/zulip,zulip/zulip,synicalsyntax/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,tommyip/zulip,shubhamdhama/zulip,synicalsyntax/zulip,andersk/zulip,eeshangarg/zulip,shubhamdhama/zulip,zulip/zulip,shubhamdhama/zulip,rht/zulip,punchagan/zulip,rishig/zulip,zulip/zulip,rht/zulip,synicalsyntax/zulip,andersk/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,eeshangarg/zulip,brainwane/zulip,kou/zulip,synicalsyntax/zulip,tommyip/zulip,tommyip/zulip,tommyip/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,andersk/zulip,tommyip/zulip,eeshangarg/zulip,brainwane/zulip,zulip/zulip,synicalsyntax/zulip,zulip/zulip,hackerkid/zulip,brainwane/zulip,brainwane/zulip,showell/zulip,timabbott/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,rishig/zulip,hackerkid/zulip,showell/zulip,hackerkid/zulip,shubhamdhama/zulip,showell/zulip,kou/zulip,punchagan/zulip,kou/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,rht/zulip,rishig/zulip,rishig/zulip,andersk/zulip,rht/zulip,rishig/zulip,zulip/zulip,brainwane/zulip,shubhamdhama/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,eeshangarg/zulip,hackerkid/zulip,tommyip/zulip,tommyip/zulip,punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,rishig/zulip,zulip/zulip,timabbott/zulip,shubhamdhama/zulip,punchagan/zulip,timabbott/zulip,andersk/zulip