Component Styles
Angular applications are styled with standard CSS. That means you can apply everything you know about CSS stylesheets, selectors, rules, and media queries directly to Angular applications.
Additionally, Angular can bundle component styles with components, enabling a more modular design than regular stylesheets.
This page describes how to load and apply these component styles.
You can run the
Using component styles
For every Angular component you write, you may define not only an HTML template, but also the CSS styles that go with that template, specifying any selectors, rules, and media queries that you need.
One way to do this is to set the styles
property in the component metadata.
The styles
property takes an array of strings that contain CSS code.
Usually you give it one string, as in the following example:
@Component({
selector: 'app-root',
template: `
<h1>Tour of Heroes</h1>
<app-hero-main [hero]="hero"></app-hero-main>
`,
styles: ['h1 { font-weight: normal; }']
})
export class HeroAppComponent {
/* . . . */
}
Style scope
The styles specified in @Component
metadata apply only within the template of that component.
They are not inherited by any components nested within the template nor by any content projected into the component.
In this example, the h1
style applies only to the HeroAppComponent
,
not to the nested HeroMainComponent
nor to <h1>
tags anywhere else in the application.
This scoping restriction is a styling modularity feature.
- You can use the CSS class names and selectors that make the most sense in the context of each component.
- Class names and selectors are local to the component and don't collide with classes and selectors used elsewhere in the application.
- Changes to styles elsewhere in the application don't affect the component's styles.
- You can co-locate the CSS code of each component with the TypeScript and HTML code of the component, which leads to a neat and tidy project structure.
- You can change or remove component CSS code without searching through the whole application to find where else the code is used.
Special selectors
Component styles have a few special selectors from the world of shadow DOM style scoping (described in the CSS Scoping Module Level 1 page on the W3C site). The following sections describe these selectors.
:host
Use the :host
pseudo-class selector to target styles in the element that hosts the component (as opposed to
targeting elements inside the component's template).
:host {
display: block;
border: 1px solid black;
}
The :host
selector is the only way to target the host element. You can't reach
the host element from inside the component with other selectors because it's not part of the
component's own template. The host element is in a parent component's template.
Use the function form to apply host styles conditionally by
including another selector inside parentheses after :host
.
The next example targets the host element again, but only when it also has the active
CSS class.
:host(.active) {
border-width: 3px;
}
:host-context
Sometimes it's useful to apply styles based on some condition outside of a component's view.
For example, a CSS theme class could be applied to the document <body>
element, and
you want to change how your component looks based on that.
Use the :host-context()
pseudo-class selector, which works just like the function
form of :host()
. The :host-context()
selector looks for a CSS class in any ancestor of the component host element,
up to the document root. The :host-context()
selector is useful when combined with another selector.
The following example applies a background-color
style to all <h2>
elements inside the component, only
if some ancestor element has the CSS class theme-light
.
:host-context(.theme-light) h2 {
background-color: #eef;
}
(deprecated) /deep/
, >>>
, and ::ng-deep
Component styles normally apply only to the HTML in the component's own template.
Use the /deep/
shadow-piercing descendant combinator to force a style down through the child
component tree into all the child component views.
The /deep/
combinator works to any depth of nested components, and it applies to both the view
children and content children of the component.
The following example targets all <h3>
elements, from the host element down
through this component to all of its child elements in the DOM.
:host /deep/ h3 {
font-style: italic;
}
The /deep/
combinator also has the aliases >>>
, and ::ng-deep
.
Use /deep/
, >>>
and ::ng-deep
only with emulated view encapsulation.
Emulated is the default and most commonly used view encapsulation. For more information, see the
Controlling view encapsulation section.
The shadow-piercing descendant combinator is deprecated and support is being removed from major browsers and tools.
As such we plan to drop support in Angular (for all 3 of /deep/
, >>>
and ::ng-deep
).
Until then ::ng-deep
should be preferred for a broader compatibility with the tools.
Loading component styles
There are several ways to add styles to a component:
- By setting
styles
orstyleUrls
metadata. - Inline in the template HTML.
- With CSS imports.
The scoping rules outlined earlier apply to each of these loading patterns.
Styles in component metadata
You can add a styles
array property to the @Component
decorator.
Each string in the array defines some CSS for this component.
@Component({
selector: 'app-root',
template: `
<h1>Tour of Heroes</h1>
<app-hero-main [hero]="hero"></app-hero-main>
`,
styles: ['h1 { font-weight: normal; }']
})
export class HeroAppComponent {
/* . . . */
}
Reminder: these styles apply only to this component. They are not inherited by any components nested within the template nor by any content projected into the component.
The CLI defines an empty styles
array when you create the component with the --inline-style
flag.
ng generate component hero-app --inline-style
Style files in component metadata
You can load styles from external CSS files by adding a styleUrls
property
to a component's @Component
decorator:
Reminder: the styles in the style file apply only to this component. They are not inherited by any components nested within the template nor by any content projected into the component.
You can specify more than one styles file or even a combination of styles
and styleUrls
.
The CLI creates an empty styles file for you by default and references that file in the component's generated styleUrls
.
ng generate component hero-app
Template inline styles
You can embed CSS styles directly into the HTML template by putting them
inside <style>
tags.
Template link tags
You can also write <link>
tags into the component's HTML template.
When building with the CLI, be sure to include the linked style file among the assets to be copied to the server as described in the CLI documentation.
Once included, the CLI will include the stylesheet, whether the link tag's href URL is relative to the application root or the component file.
CSS @imports
You can also import CSS files into the CSS files using the standard CSS @import
rule.
For details, see @import
on the MDN site.
In this case, the URL is relative to the CSS file into which you're importing.
/* The AOT compiler needs the `./` to show that this is local */
@import './hero-details-box.css';
External and global style files
When building with the CLI, you must configure the angular.json
to include all external assets, including external style files.
Register global style files in the styles
section which, by default, is pre-configured with the global styles.css
file.
See the CLI documentation to learn more.
Non-CSS style files
If you're building with the CLI,
you can write style files in sass, less, or stylus and specify those files in the @Component.styleUrls
metadata with the appropriate extensions (.scss
, .less
, .styl
) as in the following example:
@Component({
selector: 'app-root',
templateUrl: './app.component.html',
styleUrls: ['./app.component.scss']
})
...
The CLI build process runs the pertinent CSS preprocessor.
When generating a component file with ng generate component
, the CLI emits an empty CSS styles file (.css
) by default.
You can configure the CLI to default to your preferred CSS preprocessor
as explained in the CLI documentation.
Style strings added to the @Component.styles
array must be written in CSS because the CLI cannot apply a preprocessor to inline styles.
View encapsulation
As discussed earlier, component CSS styles are encapsulated into the component's view and don't affect the rest of the application.
To control how this encapsulation happens on a per component basis, you can set the view encapsulation mode in the component metadata. Choose from the following modes:
-
ShadowDom
view encapsulation uses the browser's native shadow DOM implementation (see Shadow DOM on the MDN site) to attach a shadow DOM to the component's host element, and then puts the component view inside that shadow DOM. The component's styles are included within the shadow DOM. -
Native
view encapsulation uses a now deprecated version of the browser's native shadow DOM implementation - learn about the changes. -
Emulated
view encapsulation (the default) emulates the behavior of shadow DOM by preprocessing (and renaming) the CSS code to effectively scope the CSS to the component's view. For details, see Appendix 1. -
None
means that Angular does no view encapsulation. Angular adds the CSS to the global styles. The scoping rules, isolations, and protections discussed earlier don't apply. This is essentially the same as pasting the component's styles into the HTML.
To set the components encapsulation mode, use the encapsulation
property in the component metadata:
// warning: few browsers support shadow DOM encapsulation at this time
encapsulation: ViewEncapsulation.Native
ShadowDom
view encapsulation only works on browsers that have native support
for shadow DOM (see Shadow DOM v1 on the
Can I use site). The support is still limited,
which is why Emulated
view encapsulation is the default mode and recommended
in most cases.
Inspecting generated CSS
When using emulated view encapsulation, Angular preprocesses all component styles so that they approximate the standard shadow CSS scoping rules.
In the DOM of a running Angular application with emulated view encapsulation enabled, each DOM element has some extra attributes attached to it:
<hero-details _nghost-pmm-5>
<h2 _ngcontent-pmm-5>Mister Fantastic</h2>
<hero-team _ngcontent-pmm-5 _nghost-pmm-6>
<h3 _ngcontent-pmm-6>Team</h3>
</hero-team>
</hero-detail>
There are two kinds of generated attributes:
- An element that would be a shadow DOM host in native encapsulation has a
generated
_nghost
attribute. This is typically the case for component host elements. - An element within a component's view has a
_ngcontent
attribute that identifies to which host's emulated shadow DOM this element belongs.
The exact values of these attributes aren't important. They are automatically
generated and you never refer to them in application code. But they are targeted
by the generated component styles, which are in the <head>
section of the DOM:
[_nghost-pmm-5] {
display: block;
border: 1px solid black;
}
h3[_ngcontent-pmm-6] {
background-color: white;
border: 1px solid #777;
}
These styles are post-processed so that each selector is augmented
with _nghost
or _ngcontent
attribute selectors.
These extra selectors enable the scoping rules described in this page.