modal: Mark submit button CSS `color` property as important.
modal: Mark submit button CSS `color` property as important.

This is necessary to override the global `color` property defined
for disabled buttons in night mode.

kou/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,kou/zulip,andersk/zulip,kou/zulip,rht/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip