docassemble users --
Version 0.2.50, which was just released, contains an upgrade of the user interface from Bootstrap 3.3 to Bootstrap 4.0.0. This means that when you upgrade to 0.2.50, the user interface will look significantly different.
Your screen may also render incorrectly until you do Ctrl-shift-R or Shift-F5 to force a complete reload.
If you have written any custom CSS, you may need to rewrite your CSS to adapt to the changes.
You can now use any of the Bootstrap 4 themes at https://bootswatch.com/ and other sites (see the bootstrap theme Configuration directive).