Bootstrap might be a great way to get started quickly. However, sometimes, developers get lazy and do not bother to change the default look. This leaves a poor impression on your users who might find your site's appearance a little too familiar and uninteresting.
Bootstrap 4 comes with plenty of options to improve its visual appeal. You can create a file called custom.scss where you can customize everything from theme colors to grid breakpoints. The documentation explains how you can set up the build system to compile these files down to the style sheets.
Thanks to the huge community around Bootstrap, there are also several sites, such as bootswatch.com, which have themed style sheets, that are drop-in replacements ...
