We have it set to `1` right now just to avoid compilation errors, but
it’s been replaced everywhere with our new spacer classes anywho. We’ll
likely want to remap that var to custom component vars though (e.g.,
`$pagination-margin` instead of `$spacer-y`).

Flagged upstream in bootstrap-sass by scss-lint

Refactor alerts to have a base class, but no default class, thus requiring a modifier class at all times

fixes #9310: alerts aren't dismissable by default, now requires .alert-dismissable if you need a close button

Added padding variable for alerts and changed customize.html Warning state (which doesn't exist anymore)

Resolves https://github.com/twbs/bootstrap/issues/9014. updates mixins to consistently use semicolons as argument separator. Rebuild to confirm, no diff in compiled CSS.

Moved alerts, badges, button groups, buttons, carousel, close to
variables.less and customize.html

* No more children selectors to set all links in alerts as a special color because buttons and more wrongly inherited color
* Adds .alert-link for easy styling in any alert

* Instead of 20px as @line-height-base, use 1.5
* Update typographic scale for headings to use unitless as well--required some twerking of decimals a bit and some rounding
* Introduce new @line-height-computed value, which takes base font-size and multiplies it by 1.5, for use in padding and margin on components