compose: Make compose alerts dark-mode compatible.
compose: Make compose alerts dark-mode compatible.

This makes all the alerts in the compose box compatible with dark mode
by choosing different colors and fixing borders to be properly
pronounced, along with removing text shadows that make text unreadable.

brainwane/zulip,andersk/zulip,dhcrzf/zulip,shubhamdhama/zulip,punchagan/zulip,jackrzhang/zulip,eeshangarg/zulip,synicalsyntax/zulip,mahim97/zulip,rht/zulip,shubhamdhama/zulip,kou/zulip,jackrzhang/zulip,rht/zulip,mahim97/zulip,showell/zulip,timabbott/zulip,synicalsyntax/zulip,dhcrzf/zulip,mahim97/zulip,synicalsyntax/zulip,zulip/zulip,dhcrzf/zulip,tommyip/zulip,shubhamdhama/zulip,zulip/zulip,eeshangarg/zulip,dhcrzf/zulip,eeshangarg/zulip,rishig/zulip,showell/zulip,punchagan/zulip,kou/zulip,kou/zulip,tommyip/zulip,andersk/zulip,timabbott/zulip,brainwane/zulip,zulip/zulip,tommyip/zulip,eeshangarg/zulip,andersk/zulip,brainwane/zulip,andersk/zulip,zulip/zulip,brainwane/zulip,rishig/zulip,hackerkid/zulip,andersk/zulip,synicalsyntax/zulip,andersk/zulip,showell/zulip,hackerkid/zulip,timabbott/zulip,showell/zulip,rishig/zulip,punchagan/zulip,eeshangarg/zulip,timabbott/zulip,tommyip/zulip,punchagan/zulip,mahim97/zulip,punchagan/zulip,kou/zulip,rht/zulip,rishig/zulip,jackrzhang/zulip,dhcrzf/zulip,timabbott/zulip,timabbott/zulip,jackrzhang/zulip,tommyip/zulip,jackrzhang/zulip,brainwane/zulip,synicalsyntax/zulip,timabbott/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,kou/zulip,hackerkid/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,jackrzhang/zulip,hackerkid/zulip,kou/zulip,synicalsyntax/zulip,rishig/zulip,shubhamdhama/zulip,brainwane/zulip,tommyip/zulip,dhcrzf/zulip,rishig/zulip,punchagan/zulip,hackerkid/zulip,eeshangarg/zulip,rht/zulip,hackerkid/zulip,zulip/zulip,shubhamdhama/zulip,tommyip/zulip,andersk/zulip,mahim97/zulip,hackerkid/zulip,showell/zulip,zulip/zulip,jackrzhang/zulip,mahim97/zulip,rishig/zulip,shubhamdhama/zulip,dhcrzf/zulip,rht/zulip,shubhamdhama/zulip,showell/zulip,rht/zulip,brainwane/zulip,kou/zulip