npm package: @loipham/material-theme
Description: The Material Components for the web theming system
Latest version: 14.0.4

<!--docs:
title: "Theme"
layout: detail
section: components
excerpt: "Color theming for MDC Web components."
iconId: theme
path: /catalog/theme/
-->

# Theme

The Material Design color system can be used to create a color scheme that reflects your brand or style.

## Design & API Documentation

<ul class="icon-list">
  <li class="icon-list-item icon-list-item--spec">
    <a href="https://material.io/go/design-theming">Material Design guidelines: Color</a>
  </li>
</ul>

## Installation

```
npm install @loipham/material-theme
```

## Usage

### Color Scheme

You can define the theme color variables before importing any MDC Web components:

```scss
@use "@loipham/material-theme" with (
  $primary: #fcb8ab,
  $secondary: #feeae6,
  $on-primary: #442b2d,
  $on-secondary: #442b2d,
);
@use "@loipham/material-button/mdc-button";
```

We suggest you follow the Web Content Accessibility Guidelines 2.0 when picking the values for on-primary, on-secondary, etc. These values should be accessible on top of the corresponding value, e.g. primary and secondary.

https://www.w3.org/TR/WCAG20

### Advanced customization

Color scheme will only get you 80% of the way to a well-designed app. Inevitably there will be some components that do not work "out of the box". To fix problems with accessibility and design, we suggest you use our Sass mixins, such as `button.filled-accessible()`. For more information, consult the documentation for each component.

### Text styles

The text styles (referred to as `<TEXT_STYLE>` below) used in the color system:

Text style | Description
--- | ---
`primary` | Used for most text (e.g., `text-primary-on-light`)
`secondary` | Used for text which is lower in the visual hierarchy (e.g., `text-secondary-on-light`)
`hint` | Used for text hints, such as those in text fields and labels (e.g., `text-hint-on-light`)
`disabled` | Used for text in disabled components and content (e.g., `text-disabled-on-light`)
`icon` | Used for icons (e.g., `text-icon-on-light`)

Here are the example usages of `primary` text style:

  * CSS Custom property: `--mdc-theme-text-primary-on-light`
  * Class name: `mdc-theme--text-primary-on-light`
  * Property name used in Sass: `text-primary-on-light`

### Non-Sass customization

Only a very limited number of Material Design color customization features are supported for non-Sass clients. They are a set of CSS custom properties, and a set of CSS classes.

#### CSS Custom Properties

CSS Custom property | Description
--- | ---
`--mdc-theme-primary` | The theme primary color
`--mdc-theme-secondary` | The theme secondary color
`--mdc-theme-background` | The theme background color
`--mdc-theme-surface` | The theme surface color
`--mdc-theme-on-primary` | Text color on top of a primary background
`--mdc-theme-on-secondary` | Text color on top of a secondary background
`--mdc-theme-on-surface` | Text color on top of a surface background
`--mdc-theme-text-<TEXT_STYLE>-on-light` | Text color for TEXT_STYLE on top of light background. Please see [Text styles section](#text-styles).
`--mdc-theme-text-<TEXT_STYLE>-on-dark` | Text color for TEXT_STYLE on top of dark background. Please see [Text styles section](#text-styles).

#### CSS Classes

CSS Class | Description
--- | ---
`mdc-theme--primary` | Sets the text color to the theme primary color
`mdc-theme--secondary` | Sets the text color to the theme secondary color
`mdc-theme--background` | Sets the background color to the theme background color
`mdc-theme--surface` | Sets the surface color to the theme surface color
`mdc-theme--on-primary` | Sets the text color to the theme on-primary color
`mdc-theme--on-secondary` | Sets the text color to the theme on-secondary color
`mdc-theme--on-surface` | Sets the text color to the theme on-surface color
`mdc-theme--primary-bg` | Sets the background color to the theme primary color
`mdc-theme--secondary-bg` | Sets the background color to the theme secondary color
`mdc-theme--text-<TEXT_STYLE>-on-light` | Sets text to a suitable color for TEXT_STYLE on top of light background. Please see [Text styles section](#text-styles).
`mdc-theme--text-<TEXT_STYLE>-on-dark` | Sets text to a suitable color for TEXT_STYLE on top of dark background. Please see [Text styles section](#text-styles).

### Sass Mixins, Variables, and Functions

Mixin | Description
--- | ---
`property($property, $value, $gss, $important)` | Applies a dynamic value to the specified property. The value may be a standard CSS value, a custom property Map, or a Material theme key.

#### Material theme keys with `theme.property()`

Material theme key names below can be used as the `$value` argument for the `theme.property()` mixin. Some keys are dynamic, and change context depending on other key values. Keys may also translate to custom properties for dynamic runtime theming.

Key Name | Description
--- | ---
`primary` | The theme primary color
`secondary` | The theme secondary color
`background` | The theme background color
`surface` | The theme surface color
`text-<TEXT_STYLE>-on-light` | TEXT_STYLE on top of a light background. Please see [Text styles section](#text-styles).
`text-<TEXT_STYLE>-on-dark` | TEXT_STYLE on top of a dark background. Please see [Text styles section](#text-styles).
`on-primary` | A text/iconography color that is usable on top of primary color
`on-secondary` | A text/iconography color that is usable on top of secondary color
`on-surface` | A text/iconography color that is usable on top of surface color

#### Custom properties with `theme.property()`

The `theme.property()` mixin also accepts a custom property Map for the `$value` argument. The map must contain a `varname` key with the name of the custom property, and an optional `fallback` key with the value of the custom property.

Use the `@loipham/material-theme/custom-properties` module to create custom property Maps.

For example, the following Sass...

```scss
@use "@loipham/material-theme";
@use "@loipham/material-theme/custom-properties";

.foo {
  @include theme.property(color, custom-properties.create(--foo-color, red));
}
```

...will produce the following CSS...

```
.foo {
  color: red;
  color: var(--foo-color, red);
}
```

The above output CSS will apply the `fallback` field's value for all supported browsers (including IE11) while allowing for CSS custom property use as a progressive enhancement. Browsers like IE11 that do not support CSS custom properties will apply the `color: red;` and ignore the `color: var(--foo-color, red);`. This argument type is intended for clients who need custom color application outside of the existing theme properties.

#### `theme.luminance($color)`

Calculates the luminance value (0 - 1) of a given color.

```scss
@debug theme.luminance(#9c27b0); // 0.11654
```

#### `theme.contrast($back, $front)`

Calculates the contrast ratio between two colors.

```scss
@debug theme.contrast(#9c27b0, #000); // 3.33071
```

#### `theme.tone($color)`

Determines whether the given color is "light" or "dark".

If the input color is a string literal equal to `"light"` or `"dark"`, it will be returned verbatim.

```scss
@debug theme.tone(#9c27b0); // dark
@debug theme.tone(light);   // light
```

#### `theme.contrast-tone($color)`

Determines whether to use light or dark text on top of a given color.

```scss
@debug theme.contrast-tone(#9c27b0); // light
```

#### `theme.accessible-ink-color($fill-color, $text-style: primary)`

Returns an accessible ink color that has sufficient contrast against the given fill color.

Params:

- `$fill-color`: Supports the same values as `theme.prop-value`
- `$text-style`: Value must be one of `primary`, `secondary`, `hint`, `disabled`, `icon` (see `$text-colors`)

> NOTE: This function is defined in `_variables.scss` instead of `_functions.scss` to avoid circular imports.

```scss
@debug theme.accessible-ink-color(secondary); // rgba(0, 0, 0, .87) (text-primary-on-light)
@debug theme.accessible-ink-color(blue);      // white              (text-primary-on-dark)
```
#### `theme.text-emphasis($emphasis)`

Returns opacity value for given emphasis.

Params:

- `$emphasis`: Type of emphasis such as `high`, `medium` & `disabled`.

```scss
@debug theme.text-emphasis(high); // .87
@debug theme.text-emphasis(disabled); // .38
```