Messages style update

[antonellasevero]

Problem/Motivation

Recent interviews and research exposed pain points around Drupal's admin experience of looking and feeling dated, especially compared to our competitors, and universally cited that choosing a more modern-looking admin theme instantly led to Drupal being better-perceived by said users.
There was an amazing community effort to Create a Style Guide For Seven that vastly improved its look + feel compared to the original, but Design best practices and Drupal functionality have moved on since then.

Specification

Quick overview

This image is just a quick overview for messages specs. Please use the Figma link to full specification as the main resource for specks.

Full specification

FIGMA: https://www.figma.com/file/OqWgzAluHtsOd5uwm1lubFeH/Design-system?node-id=2477%3A319
This link is anchored to the board with the full specification. As an anonymous user you can see the design, but to actually be able to pick colors and sizes please login on Figma.

Remaining tasks

• Update patch styling to include time inputs
• Accessibility review
• LTR review (Left to right)

User interface changes

All messages styles will be changed, no functional differences.

Test Pages

/admin/appearance
/admin/modules
/admin/modules/update (click on Check Manually and wait for result)
/admin/reports/status (click on RUN CRON and wait for result)