Bootstrap with css modules

Theming Bootstrap

Customize Bootstrap 4 with our new built-in Sass variables for global style preferences for easy theming and component changes.

Introduction

In Bootstrap 3, theming was largely driven by variable overrides in LESS, custom CSS, and a separate theme stylesheet that we included in our dist files. With some effort, one could completely redesign the look of Bootstrap 3 without touching the core files. Bootstrap 4 provides a familiar, but slightly different approach.

Now, theming is accomplished by Sass variables, Sass maps, and custom CSS. There’s no more dedicated theme stylesheet; instead, you can enable the built-in theme to add gradients, shadows, and more.

Sass

Utilize our source Sass files to take advantage of variables, maps, mixins, and more.

File structure

Whenever possible, avoid modifying Bootstrap’s core files. For Sass, that means creating your own stylesheet that imports Bootstrap so you can modify and extend it. Assuming you’re using a package manager like npm, you’ll have a file structure that looks like this:

your-project/ ├── scss │ └── custom.scss └── node_modules/ └── bootstrap ├── js └── scss

If you’ve downloaded our source files and aren’t using a package manager, you’ll want to manually setup something similar to that structure, keeping Bootstrap’s source files separate from your own.

your-project/ ├── scss │ └── custom.scss └── bootstrap/ ├── js └── scss

Importing

In your custom.scss , you’ll import Bootstrap’s source Sass files. You have two options: include all of Bootstrap, or pick the parts you need. We encourage the latter, though be aware there are some requirements and dependencies across our components. You also will need to include some JavaScript for our plugins.

// Custom.scss // Option A: Include all of Bootstrap @import "node_modules/bootstrap/scss/bootstrap";

// Custom.scss // Option B: Include parts of Bootstrap // Required @import "node_modules/bootstrap/scss/functions"; @import "node_modules/bootstrap/scss/variables"; @import "node_modules/bootstrap/scss/mixins"; // Optional @import "node_modules/bootstrap/scss/reboot"; @import "node_modules/bootstrap/scss/type"; @import "node_modules/bootstrap/scss/images"; @import "node_modules/bootstrap/scss/code"; @import "node_modules/bootstrap/scss/grid";

With that setup in place, you can begin to modify any of the Sass variables and maps in your custom.scss . You can also start to add parts of Bootstrap under the // Optional section as needed. We suggest using the full import stack from our bootstrap.scss file as your starting point.

Variable defaults

Every Sass variable in Bootstrap 4 includes the !default flag allowing you to override the variable’s default value in your own Sass without modifying Bootstrap’s source code. Copy and paste variables as needed, modify their values, and remove the !default flag. If a variable has already been assigned, then it won’t be re-assigned by the default values in Bootstrap.

Variable overrides within the same Sass file can come before or after the default variables. However, when overriding across Sass files, your overrides must come before you import Bootstrap’s Sass files.

Here’s an example that changes the background-color and color for the when importing and compiling Bootstrap via npm:

// Your variable overrides $body-bg: #000; $body-color: #111; // Bootstrap and its default variables @import "node_modules/bootstrap/scss/bootstrap";

Repeat as necessary for any variable in Bootstrap, including the global options below.

Maps and loops

Bootstrap 4 includes a handful of Sass maps, key value pairs that make it easier to generate families of related CSS. We use Sass maps for our colors, grid breakpoints, and more. Just like Sass variables, all Sass maps include the !default flag and can be overridden and extended.

Some of our Sass maps are merged into empty ones by default. This is done to allow easy expansion of a given Sass map, but comes at the cost of making removing items from a map slightly more difficult.

Modify map

To modify an existing color in our $theme-colors map, add the following to your custom Sass file:

$theme-colors: ( "primary": #0074d9, "danger": #ff4136 );

Add to map

To add a new color to $theme-colors , add the new key and value:

$theme-colors: ( "custom-color": #900 );

Remove from map

To remove colors from $theme-colors , or any other map, use map-remove :

$theme-colors: map-remove($theme-colors, "success", "info", "danger");

Required keys

Bootstrap assumes the presence of some specific keys within Sass maps as we used and extend these ourselves. As you customize the included maps, you may encounter errors where a specific Sass map’s key is being used.

For example, we use the primary , success , and danger keys from $theme-colors for links, buttons, and form states. Replacing the values of these keys should present no issues, but removing them may cause Sass compilation issues. In these instances, you’ll need to modify the Sass code that makes use of those values.

Functions

Bootstrap utilizes several Sass functions, but only a subset are applicable to general theming. We’ve included three functions for getting values from the color maps:

@function color($key: "blue")  @return map-get($colors, $key); > @function theme-color($key: "primary")  @return map-get($theme-colors, $key); > @function gray($key: "100")  @return map-get($grays, $key); >

These allow you to pick one color from a Sass map much like how you’d use a color variable from v3.

.custom-element  color: gray("100"); background-color: theme-color("dark"); >

We also have another function for getting a particular level of color from the $theme-colors map. Negative level values will lighten the color, while higher levels will darken.

@function theme-color-level($color-name: "primary", $level: 0)  $color: theme-color($color-name); $color-base: if($level > 0, #000, #fff); $level: abs($level); @return mix($color-base, $color, $level * $theme-color-interval); >

In practice, you’d call the function and pass in two parameters: the name of the color from $theme-colors (e.g., primary or danger) and a numeric level.

.custom-element  color: theme-color-level(primary, -10); >

Additional functions could be added in the future or your own custom Sass to create level functions for additional Sass maps, or even a generic one if you wanted to be more verbose.

Color contrast

One additional function we include in Bootstrap is the color contrast function, color-yiq . It utilizes the YIQ color space to automatically return a light ( #fff ) or dark ( #111 ) contrast color based on the specified base color. This function is especially useful for mixins or loops where you’re generating multiple classes.

For example, to generate color swatches from our $theme-colors map:

@each $color, $value in $theme-colors  .swatch-#$color>  color: color-yiq($value); > >

It can also be used for one-off contrast needs:

.custom-element  color: color-yiq(#000); // returns `color: #fff` >

You can also specify a base color with our color map functions:

.custom-element  color: color-yiq(theme-color("dark")); // returns `color: #fff` >

Sass options

Customize Bootstrap 4 with our built-in custom variables file and easily toggle global CSS preferences with new $enable-* Sass variables. Override a variable’s value and recompile with npm run test as needed.

You can find and customize these variables for key global options in our _variables.scss file.

Variable	Values	Description
$spacer	1rem (default), or any value > 0	Specifies the default spacer value to programmatically generate our spacer utilities.
$enable-rounded	true (default) or false	Enables predefined border-radius styles on various components.
$enable-shadows	true or false (default)	Enables predefined box-shadow styles on various components.
$enable-gradients	true or false (default)	Enables predefined gradients via background-image styles on various components.
$enable-transitions	true (default) or false	Enables predefined transition s on various components.
$enable-hover-media-query	true or false (default)	Deprecated
$enable-grid-classes	true (default) or false	Enables the generation of CSS classes for the grid system (e.g., .container , .row , .col-md-1 , etc.).
$enable-caret	true (default) or false	Enables pseudo element caret on .dropdown-toggle .
$enable-print-styles	true (default) or false	Enables styles for optimizing printing.

Color

Many of Bootstrap’s various components and utilities are built through a series of colors defined in a Sass map. This map can be looped over in Sass to quickly generate a series of rulesets.

All colors

All colors available in Bootstrap 4, are available as Sass variables and a Sass map in our scss/_variables.scss file. This will be expanded upon in subsequent minor releases to add additional shades, much like the grayscale palette we already include.

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