Firefox requires a width and flex-basis value to size the input field correctly. Despite the width being 1%, the input will size correctly at all parent widths.

http://codepen.io/zalog/pen/bpMJmv

Fixes #21023.

Uses some math functions to determine what the offset should be. This is helpful for those who customize the size of their indicators and still want them vertically centered.

Fixes #20730.

This change computes the minimum needed height of what a single line of text would be for the custom checkboxes/radios. This is required because our custom control indicators are positioned absolutely, meaning they cannot be clearfixed or anything like that. Using a computed value means it should scale nicely in case of customization

Fixes #20927.

.col-xs-auto, .col-sm-auto, etc.

Websites might use different weights such as medium or thin or use light as default weight instead of normal.
Also referenced: #18605 and #16170.

- Adds six new utils for vertical-align property
- Documents the additional classes in the utils docs

Follow up to 6e8ce0c7. Uses the breakpoint-next mixin to snag the next breakpoint in the media query for proper styling.

- Moves .navbar-brand margin and float to media queries
- Replaces the static media queries with an each loop to generate all the needed classes

Fully fixes #20395

Matches the changes from #20874 to the regular select element. This is really only necessary for IE and Edge near as I can tell. Fixes #20810.