What to do with testing css animations?

Problem/Motivation

Due to various CSS transitions/animations/transforms, checking the visibility of elements is not always correct. This leads to random fails.

Examples:

• https://www.drupal.org/node/2901626

Proposed resolution

1. Additional conditions for checking visibility, like #2848177-14: More \Drupal\Tests\outside_in\FunctionalJavascript\OutsideInBlockFormTest random fails
2. Disable these CSS rules for testing, like #2901626-5: The Returned of the \Drupal\Tests\outside_in\FunctionalJavascript\OutsideInBlockFormTest random fails
3. Finding another solution (maybe wait to #2775653: [PP-2] JavascriptTests with webDriver)

Remaining tasks

User interface changes

API changes

Data model changes