Bootstrap 4 replaced floats with flexbox utilities, simplified cards and navbars, and removed jQuery as a hard dependency path toward v5. It was the last major version many Bootstrap 3 sites migrated to before TailwindA utility-first CSS framework — compose designs from small classes instead of custom stylesheets. gained share.

Bootstrap 4 modernized the framework for flexbox-era layouts.

Flexbox grids and rebuilt components kept Bootstrap the default admin UIUser interface — the parts of software people see and interact with. kit.