left sidebar: Fix gaps between hover areas.
left sidebar: Fix gaps between hover areas.

A somewhat recent refactoring of the left sidebar had introduced a gap
between the hover areas that looked off; this fixes this with a slight
rearrangement with where the 1px of space between elements lives.

Fixes #12508.

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