Drop support for Bootstrap 3 (EOL'd) and upgrade to the latest Bootstrap version
Drop support for Bootstrap 3 and upgrade to the latest Bootstrap version.
Because Bootstrap 3 was released 10 years ago. CiviCRM should not be shipping with known out of date software libraries.
Bootstrap 3 is End-of-life as of 2019-07-24, reference https://github.com/twbs/release#release-schedule