Bootstrap - CSS variables

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This chapter discusses about all the CSS variables provided by Bootstrap, that help in fast and customized design and development of applications.

The compiled CSS of Bootstrap consists of a plethora of CSS custom properties (variables) that allow for instant customization without the need to recompile Sass, wherein commonly used values such as theme colors, breakpoints, and primary font stacks are easily accessible during browser inspection, code sandbox operation, or general prototyping.

All the custom variables provided by Bootstrap are prefixed with bs-, so that there is no conflict with any other third-party CSS.

Root variables

Root variables are the variables that can be accessed from anywhere, Bootstrap’s CSS is loaded. These variables are located in the _root.scss file and also included in the compiled dist files

Default variables

The CSS variables that are accessible everywhere, irrespective of the color mode, are the default variables.

    :root,
    [data-bs-theme=light] {
    --bs-blue: #0d6efd;
    --bs-indigo: #6610f2;
    --bs-purple: #6f42c1;
    --bs-pink: #d63384;
    --bs-red: #dc3545;
    --bs-orange: #fd7e14;
    --bs-yellow: #ffc107;
    --bs-green: #198754;
    --bs-teal: #20c997;
    --bs-cyan: #0dcaf0;
    --bs-black: #000;
    --bs-white: #fff;
    --bs-gray: #6c757d;
    --bs-gray-dark: #343a40;
    --bs-gray-100: #f8f9fa;
    --bs-gray-200: #e9ecef;
    --bs-gray-300: #dee2e6;
    --bs-gray-400: #ced4da;
    --bs-gray-500: #adb5bd;
    --bs-gray-600: #6c757d;
    --bs-gray-700: #495057;
    --bs-gray-800: #343a40;
    --bs-gray-900: #212529;
    --bs-primary: #0d6efd;
    --bs-secondary: #6c757d;
    --bs-success: #198754;
    --bs-info: #0dcaf0;
    --bs-warning: #ffc107;
    --bs-danger: #dc3545;
    --bs-light: #f8f9fa;
    --bs-dark: #212529;
    --bs-primary-rgb: 13, 110, 253;
    --bs-secondary-rgb: 108, 117, 125;
    --bs-success-rgb: 25, 135, 84;
    --bs-info-rgb: 13, 202, 240;
    --bs-warning-rgb: 255, 193, 7;
    --bs-danger-rgb: 220, 53, 69;
    --bs-light-rgb: 248, 249, 250;
    --bs-dark-rgb: 33, 37, 41;
    --bs-primary-text-emphasis: #052c65;
    --bs-secondary-text-emphasis: #2b2f32;
    --bs-success-text-emphasis: #0a3622;
    --bs-info-text-emphasis: #055160;
    --bs-warning-text-emphasis: #664d03;
    --bs-danger-text-emphasis: #58151c;
    --bs-light-text-emphasis: #495057;
    --bs-dark-text-emphasis: #495057;
    --bs-primary-bg-subtle: #cfe2ff;
    --bs-secondary-bg-subtle: #e2e3e5;
    --bs-success-bg-subtle: #d1e7dd;
    --bs-info-bg-subtle: #cff4fc;
    --bs-warning-bg-subtle: #fff3cd;
    --bs-danger-bg-subtle: #f8d7da;
    --bs-light-bg-subtle: #fcfcfd;
    --bs-dark-bg-subtle: #ced4da;
    --bs-primary-border-subtle: #9ec5fe;
    --bs-secondary-border-subtle: #c4c8cb;
    --bs-success-border-subtle: #a3cfbb;
    --bs-info-border-subtle: #9eeaf9;
    --bs-warning-border-subtle: #ffe69c;
    --bs-danger-border-subtle: #f1aeb5;
    --bs-light-border-subtle: #e9ecef;
    --bs-dark-border-subtle: #adb5bd;
    --bs-white-rgb: 255, 255, 255;
    --bs-black-rgb: 0, 0, 0;
    --bs-font-sans-serif: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", "Noto Sans", "Liberation Sans", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
    --bs-font-monospace: SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
    --bs-gradient: linear-gradient(180deg, rgba(255, 255, 255, 0.15), rgba(255, 255, 255, 0));
    --bs-body-font-family: var(--bs-font-sans-serif);
    --bs-body-font-size: 1rem;
    --bs-body-font-weight: 400;
    --bs-body-line-height: 1.5;
    --bs-body-color: #212529;
    --bs-body-color-rgb: 33, 37, 41;
    --bs-body-bg: #fff;
    --bs-body-bg-rgb: 255, 255, 255;
    --bs-emphasis-color: #000;
    --bs-emphasis-color-rgb: 0, 0, 0;
    --bs-secondary-color: rgba(33, 37, 41, 0.75);
    --bs-secondary-color-rgb: 33, 37, 41;
    --bs-secondary-bg: #e9ecef;
    --bs-secondary-bg-rgb: 233, 236, 239;
    --bs-tertiary-color: rgba(33, 37, 41, 0.5);
    --bs-tertiary-color-rgb: 33, 37, 41;
    --bs-tertiary-bg: #f8f9fa;
    --bs-tertiary-bg-rgb: 248, 249, 250;
    --bs-heading-color: inherit;
    --bs-link-color: #0d6efd;
    --bs-link-color-rgb: 13, 110, 253;
    --bs-link-decoration: underline;
    --bs-link-hover-color: #0a58ca;
    --bs-link-hover-color-rgb: 10, 88, 202;
    --bs-code-color: #d63384;
    --bs-highlight-bg: #fff3cd;
    --bs-border-width: 1px;
    --bs-border-style: solid;
    --bs-border-color: #dee2e6;
    --bs-border-color-translucent: rgba(0, 0, 0, 0.175);
    --bs-border-radius: 0.375rem;
    --bs-border-radius-sm: 0.25rem;
    --bs-border-radius-lg: 0.5rem;
    --bs-border-radius-xl: 1rem;
    --bs-border-radius-xxl: 2rem;
    --bs-border-radius-2xl: var(--bs-border-radius-xxl);
    --bs-border-radius-pill: 50rem;
    --bs-box-shadow: 0 0.5rem 1rem rgba(0, 0, 0, 0.15);
    --bs-box-shadow-sm: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.075);
    --bs-box-shadow-lg: 0 1rem 3rem rgba(0, 0, 0, 0.175);
    --bs-box-shadow-inset: inset 0 1px 2px rgba(0, 0, 0, 0.075);
    --bs-focus-ring-width: 0.25rem;
    --bs-focus-ring-opacity: 0.25;
    --bs-focus-ring-color: rgba(13, 110, 253, 0.25);
    --bs-form-valid-color: #198754;
    --bs-form-valid-border-color: #198754;
    --bs-form-invalid-color: #dc3545;
    --bs-form-invalid-border-color: #dc3545;
    }

Dark mode variables

Following variables are limited to the built-in dark mode of Bootstrap:

    [data-bs-theme=dark] {
        color-scheme: dark;
        --bs-body-color: #adb5bd;
        --bs-body-color-rgb: 173, 181, 189;
        --bs-body-bg: #212529;
        --bs-body-bg-rgb: 33, 37, 41;
        --bs-emphasis-color: #fff;
        --bs-emphasis-color-rgb: 255, 255, 255;
        --bs-secondary-color: rgba(173, 181, 189, 0.75);
        --bs-secondary-color-rgb: 173, 181, 189;
        --bs-secondary-bg: #343a40;
        --bs-secondary-bg-rgb: 52, 58, 64;
        --bs-tertiary-color: rgba(173, 181, 189, 0.5);
        --bs-tertiary-color-rgb: 173, 181, 189;
        --bs-tertiary-bg: #2b3035;
        --bs-tertiary-bg-rgb: 43, 48, 53;
        --bs-primary-text-emphasis: #6ea8fe;
        --bs-secondary-text-emphasis: #a7acb1;
        --bs-success-text-emphasis: #75b798;
        --bs-info-text-emphasis: #6edff6;
        --bs-warning-text-emphasis: #ffda6a;
        --bs-danger-text-emphasis: #ea868f;
        --bs-light-text-emphasis: #f8f9fa;
        --bs-dark-text-emphasis: #dee2e6;
        --bs-primary-bg-subtle: #031633;
        --bs-secondary-bg-subtle: #161719;
        --bs-success-bg-subtle: #051b11;
        --bs-info-bg-subtle: #032830;
        --bs-warning-bg-subtle: #332701;
        --bs-danger-bg-subtle: #2c0b0e;
        --bs-light-bg-subtle: #343a40;
        --bs-dark-bg-subtle: #1a1d20;
        --bs-primary-border-subtle: #084298;
        --bs-secondary-border-subtle: #41464b;
        --bs-success-border-subtle: #0f5132;
        --bs-info-border-subtle: #087990;
        --bs-warning-border-subtle: #997404;
        --bs-danger-border-subtle: #842029;
        --bs-light-border-subtle: #495057;
        --bs-dark-border-subtle: #343a40;
        --bs-heading-color: inherit;
        --bs-link-color: #6ea8fe;
        --bs-link-hover-color: #8bb9fe;
        --bs-link-color-rgb: 110, 168, 254;
        --bs-link-hover-color-rgb: 139, 185, 254;
        --bs-code-color: #e685b5;
        --bs-border-color: #495057;
        --bs-border-color-translucent: rgba(255, 255, 255, 0.15);
        --bs-form-valid-color: #75b798;
        --bs-form-valid-border-color: #75b798;
        --bs-form-invalid-color: #ea868f;
        --bs-form-invalid-border-color: #ea868f;
      }

Component variables

The usage of custom properties as local variables for various components is becoming more prevalent in Bootstrap 5. This results in a reduction of compiled CSS, prevents styles from being inherited in nested tables, and permits some customization and expansion of Bootstrap components following Sass compilation.

CSS variables are distinctively used in navbars, grids and many more. When CSS variables are assigned at base component level, it becomes easier to customize and modify it later.

Prefix

A prefix is used with most of the variables, in order to prevent any collisions with your own codebase. Every CSS variable requires --, apart from the prefix.

You can customize the prefix, using the $prefix Sass variable. It is set to bs-, by default.

Examples

CSS variables provide comparable adaptability to Sass variables; however, there is no requirement for compilation before transmitting to the browser. As an illustration, we utilize CSS variables to reset our page's font and link styles:

    body {
        font: 1rem/1.5 var(--bs-font-monospace);
    }
    a {
        color: var(--bs-red);
    }

Focus variables

By employing a blend of Sass and CSS variables, Bootstrap enables the provision of personalized :focus styles that can be selectively appended to singular components and elements. Nevertheless, the overriding of all :focus styles across the board is not currently implemented.

Default values can be set in the Sass, that can be customized before compiling.

scss/_variables.scss
    $focus-ring-width:      .25rem;
    $focus-ring-opacity:    .25;
    $focus-ring-color:      rgba($primary, $focus-ring-opacity);
    $focus-ring-blur:       0;
    $focus-ring-box-shadow: 0 0 $focus-ring-blur $focus-ring-width $focus-ring-color;

The variables are subsequently assigned to CSS variables at the :root level, which can be customized in real-time and feature options for x and y offsets, with their default fallback value being 0.

scss/_root.scss
    --#{$prefix}focus-ring-width: #{$focus-ring-width};
    --#{$prefix}focus-ring-opacity: #{$focus-ring-opacity};
    --#{$prefix}focus-ring-color: #{$focus-ring-color};

Grid breakpoints

Grid breakpoints, such as md, lg, xl, xxl are included as CSS variables (except for xs). CSS variables can not be used in media queries.