Upgrade to Bootstrap 4.3.1, see https://github.com/twbs/bootstrap/issues/27893, https://blog.getbootstrap.com/2019/02/13/bootstrap-4-3-1-and-3-4-1/ and https://blog.getbootstrap.com/2019/02/11/bootstrap-4-3-0/ for official Bootstrap docs.

Replace the following files/snippets:

• Replace: reference to all Bootstrap 4.3.1 CSS and Javascript files in head & footer.
• Using command line within the /theme folder, run: yarn
• Replace: all .css files in assets/css apart from your custom CSS files.