Bootstrap 3 is not backwards compatible with v2.x. Use this section as a general guide to upgrading from v2.x to v3.0. For a broader overview, see what’s new in the v3.0 release announcement.
This table shows the style changes between v2.x and v3.0.
We’ve added new elements and changed some existing ones. Here are the new or updated styles.
The following elements have been dropped or changed in v3.0.
Fixed-width input sizes .input-mini .input-small .input-medium .input-large .input-xlarge .input-xxlarge Use .form-control and the grid system instead.
Block level form input .input-block-level No direct equivalent, but forms controls are similar.
Nav lists .nav-list .nav-header No direct equivalent, but list groups and .panel-groups are similar.
Inline help for form controls .help-inline No exact equivalent, but .help-block is similar.
By default, text-based form controls now receive only minimal styling. For focus colors and rounded corners, apply the .form-control class on the element to style.
Text-based form controls with the .form-control class applied are now 100% wide by default. Wrap inputs inside <div class="col-*"></div> to control input widths.
.badge no longer has contextual (-success,-primary,etc..) classes.
.btn must also use .btn-default to get the “default” button.
Images are no longer responsive by default. Use .img-responsive for fluid <img> size.
The icons, now .glyphicon, are now font based. Icons also require a base and icon class (e.g. .glyphicon .glyphicon-asterisk).
Typeahead has been dropped, in favor of using Twitter Typeahead.
Modal markup has changed significantly. The .modal-header, .modal-body, and .modal-footer sections are now wrapped in .modal-content and .modal-dialog for better mobile styling and behavior. Also, you should no longer apply .hide to .modal in your markup.
As of v3.1.0, the HTML loaded by the remote modal option is now injected into the .modal-content (from v3.0.0 to v3.0.3, into the .modal) instead of into the .modal-body. This allows you to also easily vary the header and footer of the modal, not just the modal body.
For more information on upgrading to v3.0, and code snippets from the community, see Bootply.