[MM-29500] Migrate changeCSS() to CSS variable in utils/utils.jsx

[oliverJurgen]

Summary

Migrate changeCss('.app*_body #channel*view.channel-view', `background: ${theme.centerChannelBg}`) in line 620 to CSS variables. Css applied in sass/base/_structure.scss.

Ticket Link

Fixes mattermost/mattermost#15887

Jira: https://mattermost.atlassian.net/browse/MM-29500.

If I have to make changes in the PR, please do tell me. Thanks

[mattermod]

Hello @oliverJurgen,

Thanks for your pull request! A Core Committer will review your pull request soon. For code contributions, you can learn more about the review process here.

[asaadmahmood]

Please use it like this:

.channel-view {
        &#channel-view {
            background: var(--center-channel-bg);
        }
    }

Also please see if we need so much specificity or just .channel_view works.

[calebroseland]

Thanks for the PR, @oliverJurgen! Would you mind moving background to the plain .channel-view towards the bottom?

[oliverJurgen]

I applied the changes

[oliverJurgen]

@calebroseland Hello, any more changes I should do?

[calebroseland]

@oliverJurgen I think it would be a good chance to simplify and put in just .channel-view down by :80. If you wouldn't mind, that'd be great :)

[oliverJurgen]

sounds good, will do that :)

[oliverJurgen]

please check my latest change @calebroseland :)

[calebroseland]

Thanks, @oliverJurgen!

[mattermod]

This PR has been automatically labelled "stale" because it hasn't had recent activity.
A core team member will check in on the status of the PR to help with questions.
Thank you for your contribution!

/cc @jasonblais @jfrerich @emilyacook

[jasonblais]

@calebroseland @asaadmahmood is this ready to merge?

[calebroseland]

@jasonblais yes, my bad.