Not all pages will be at 100%, but most will be in the high 90s, at least. You gotta admit, that's pretty good!
Skilling is based on Drupal. Drupal separates the look-and-feel of a site from the data processing. A group of files that create the look-and-feel of a Drupal site is called a "theme."
Skilling has a custom theme based on Bootstrap 4. Bootstrap is perhaps the most widely used front-end framework on the web. The first version was released in August, 2011, and it has been under continuous development ever since.
Bootstrap 4 was a long time coming after Bootstrap 3, but was worth the wait. Implemented correctly, it complies with WCAG 2.0 (A/AA/AAA). AAA compliance is an impressive achievement. Kudos to the Bootstrap team! Bootstrap 4 also complies with Section 508 of the US Rehabilitation Act.