Changes:

• Upgrade to Bootstrap 4.5, see https://github.com/twbs/bootstrap/issues?q=project%3Atwbs%2Fbootstrap%2F18+is%3Aclosed+sort%3Aupdated-desc and https://blog.getbootstrap.com/2020/05/12/bootstrap-4-5-0/ for official Bootstrap docs.
• Upgrade to Bootstrap Icons v1.0.0-alpha4, see: https://icons.getbootstrap.com/ && elements-icons-bootstrap-icons.html

Replace the following files/snippets:

• Replace: reference to all Bootstrap 4.5 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.