unwanted CSS overrides in webapp

[michelengelen]

Describe the bug

The plugin introduces some CSS overrides which result in a wrong style being applied to the "Invite people" modals close button. The rules responsible for the override can possibly just be removed, since they have changed a fair bit.

There is a JIRA ticket for this: MM-37852

How to reproduce it

1. go to the community-server
2. select a dark theme (e.g. "Onyx")
3. open the channel header menu

3. click "Invite people" 4. Observe a close button that is hardly visible

Expected behaviour

the close button should be correctly styled

Screenshots
the close button is currently not visible

this is where it is located

Environment
mattermost community server

Additional context

same issue on another plugin: cpanato/mattermost-plugin-postmortem#18