night_mode: Fix search_icon hover regression.
night_mode: Fix search_icon hover regression.

In 9046fc103288274d74e8eb7cf5a1b4fddf6fbb46 we updated the navbar.html
file so that our css selectors did not override each other and cause
annoying problems.

Unfortunately this caused a regression in night mode where the
search_icon didn't have the correct hover effect.

This fixes the regression by adding the selectors.

zulip/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,showell/zulip,punchagan/zulip,rht/zulip,brainwane/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,zulip/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,rht/zulip,showell/zulip,punchagan/zulip,kou/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,andersk/zulip,rht/zulip,andersk/zulip,brainwane/zulip,zulip/zulip,hackerkid/zulip,brainwane/zulip,showell/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,andersk/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,rht/zulip,zulip/zulip,kou/zulip