Remove bad margin from buttons

[orhoj]

Purpose

Enhance the UI.

Changes

• Removed margin on add web3 ID credential page.
• Made allowlist header readable in dark mode.
• Made the popup menu closer to the Figma drawings. In particular it also works better in dark mode now.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.