Fix color scheme of buttons in /upgrade

- on /upgrade buttons look weird: they have two background colors, green and blue.
- on the homepage the title border looks ugly

I’m proposing a branch to fix these two issues, as people started wondering. Please review and cherry-pick what you like.

Feature Branch: web/15597-upgrade-buttons

Attachments

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Related issues

• Related to #11493 (closed)
• Related to #15114 (closed)

Original created by @u on 15597 (Redmine)