css: Add nightmode variant for fetching more messages loading indicator
css: Add nightmode variant for fetching more messages loading indicator

Fixes: #12522.

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