Bootstrap v4.0.0-alpha.6 发布了，Bootstrap是快速开发Web应用程序的前端工具包。它是一个CSS和HTML的集合，它使用了最新的浏览器技术，给你的Web开发提供了时尚的版式，表单，buttons，表格，网格系统等等。
Flexbox
is now on by default, with no fallback! This means we've dropped IE9
support, but with significant savings to our code base, simpler
components, and improved customization thanks to the power of flexbox.
Rebuilt
the navbar with flexbox in mind, leading to some structural changes,
but including more flexibility and customization. Includes updated docs,
code snippets, more responsive options. All navbars in our examples are
also using the latest markup and styles now. Also solves around 10 bugs
in the process!
Overhauled flexbox utilities and
documented them. Replaced all the previous flexbox utilities with new
ones that are named after property: value pairs (instead of creating new names for things). For example, .flex-items-between is now .justify-content-between to apply justify-content: between;. This also adds tons of new flexbox utilities for display, order, wrap, and more.
Revamped navs Sass with flexbox and updated docs. All the floats and clearfixs have been removed, .nav-inline removed (on account of display: flex inlining for us on .nav), added fill and justify options, and more.
Building
on the grid improvements from Alpha 5, you can now customize container
padding across grid breakpoints and optionally remove grid gutters with .no-gutters.
Similarly,
our flexbox grid system has new classes for automatically sizing
columns to the size of their content across viewports (e.g., you can now
apply col-xs-6, col-md-auto, and col-xl-4 to a single element).
Grid,
display, float, margin, padding, and text utility classes have been
significantly overhauled. In addition to all classes now being
responsive, the xs tier no longer requires a breakpoint
abbreviation, making for shorter and more descriptive classes and an
easier migration from v3. For example, instead of .d-xs-none, it's back to .d-none while it remains .d-{sm,md,lg,xl}-none for those breakpoints.
Renamed some .active, all .in, and all .open classes for our JavaScript powered components for more consistent naming. For example, instead it's now .collapse.show instead of .collapse.in and.show > .dropdown-menu instead of .open > .dropdown-menu to better communicate the visibility of elements.
Refactored carousel with new, simpler styles, better documentation, and less specific selectors.
Rewrote progress component without the
Fixed some unescaped #s in our SVG data URLs that are used to add vector background-images.
Renamed .tag back to .badge, like v3, to avoid conflicts with common WordPress styles.
A number of custom form enhancements and bugfixes were made. Label-less custom radios and cehckboxes, fixed SVG URLs in background-images, and more.
Updated Normalize.css to v5.0.0.
.form-check and .form-check-inline now share the same markup. Switch between the two by adding or removing .form-check-inline as a modifier.
Added support for justified navigation when in flexbox mode.
Renamed _animation.scss to _transitions.scss for clarity.
Added new color variables (e.g., $blue) for additional customization.
