[Web] Improve styling of about dialog

[waldyrious]

Feature Description

The About dialog currently has a couple minor issues that are hopefully a quick fix:

1. It should be centered in the right pane, disregarding the width of the settings sidebar, rather than centered in the entire viewport. The way it currently is possitioned, it seems to be off-center due to the app icon that appears in the background.
2. The items ("Source code", "Noto Emoji" and "Logs") should have some padding around them.
3. The app icon within the dialog should probably not have a white background.

Rationale

The current styling looks off.

Mockup

I tried making changes using the browser developer tools but unfortunately the way this is implemented isn't amenable to that approach.

Additional Context

Originally reported in the GitLab project: https://gitlab.com/famedly/fluffychat/-/issues/1153

[github-actions]

This issue is stale because it has been open for 120 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 14 days since being marked as stale.