What elements can be customized?

Bootstrap 5 is easily customizable in many ways. You can customize various options for typography, color, spacing, sizing, border radius, box shadow, and more across all components, as well as customize all the different components individually. You can also customize the helpers and utilities in many different ways. The most important elements to customize are, without doubt, the color palette and typography so that they will match that of your brand. The other aspects can then be further customized to align with your current brand guidelines or just to differentiate your user interface from all the websites that make use of the default Bootstrap styles.

JavaScript Behavior Can Be Customized Too

You generally want to customize the styles of Bootstrap, as described previously; however, the behavior of JavaScript-enabled components can also be changed from the default values. While this is not that important for the perception of your brand, it might be something to consider changing as well.