Bootstrap/site/content/docs/4.3/customize/css-variables.md

layout	title	description	group	toc
docs	CSS variables	Use Bootstrap's CSS custom properties for fast and forward-looking design and development.	customize	true

Bootstrap includes around two dozen CSS custom properties (variables) in its compiled CSS. These provide easy access to commonly used values like our theme colors and primary font stacks when working in your browser's Inspector, a code sandbox, or general prototyping.

All our custom properties are prefixed with bs- to avoid conflicts with third party CSS.

Root variables

Here are the variables we include (note that the :root is required) that can be accessed anywhere Bootstrap's CSS is loaded. They're located in our _root.scss file and included in our compiled dist files.

{{< highlight css >}} {{< root.inline >}} {{- $css := readFile "dist/css/bootstrap.css" -}} {{- $match := findRE ":root {([^}]*)}" $css 1 -}}

{{- if (eq (len $match) 0) -}} {{- errorf "Got no matches for :root in %q!" $.Page.Path -}} {{- end -}}

{{- index $match 0 -}}

{{< /root.inline >}} {{< /highlight >}}

Component variables

We're also beginning to make use of custom properties as local variables for various components. By using CSS variables in this way, we can heavily reduce our compiled CSS, ensure that table styles aren't inherited, and allow you to dynamically restyle or extend Bootstrap components without recompiling Sass.

Have a look at our table documentation for some [insight into how we're using CSS variables]({{< docsref "/content/tables#how-do-the-variants-and-accented-tables-work" >}}).

Examples

CSS variables offer similar flexibility to Sass's variables, but without the need for compilation before being served to the browser. For example, here we're resetting our page's font and link styles with CSS variables.

{{< highlight css >}} body { font: 1rem/1.5 var(--bs-font-sans-serif); } a { color: var(--bs-blue); } {{< /highlight >}}