Update the grid system so containers use width alongside a max-width: 100% for more durable layouts, fix the sm breakpoint and container dimension mismatch, and change the lg breakpoint width from 940px to 960px.
Update utilities across the board, simplifying the margin and padding syntax (e.g., now mx-autoinstead of m-x-auto), separating background and color utilities for more explicit styling, renamed .img-rounded and .img-circle to .rounded and .rounded-circle, and removed display: blockfrom .img-fluid.
Added new vertical alignment utilities.
Updated development dependencies, so be sure to update to the latest Bundler and npm versions with gem install bundler, bundle update, and npm install.
More customizable custom form controls with embedded SVGs and Sass variables.
Brand new navbar toggler control featuring an SVG background-image.
Fixed bug in our flexbox grid where columns didn't properly collapse at lower breakpoints.
Removed momentum scrolling on modals for now due to an iOS 9-10 bug.
Dozens of documentation updates and bug fixes.
CSS
#17194, #20874: Ensure selects and inputs match their heights with .form-control.
#17481: Add breakpoint-specific gutters to grid system.
#18020: Improved custom checkbox and radio alignment.
#18726, #19048: Add a margin-bottom: 0; to .card-header for use with headings.
#19784, #20701: Improve units in dropdown components and remove margin-bottom from .dropdown-header.