dark-mode: Change Stream list chevrons colors to have more contrast.
dark-mode: Change Stream list chevrons colors to have more contrast.

Fixes #7794.

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