@title
Component Styles
@intro
Learn how to apply CSS styles to components.
@description
Angular applications are styled with regular CSS. That means we can apply
everything we know about CSS stylesheets, selectors, rules, and media queries
to our Angular applications directly.
On top of this, Angular has the ability to bundle *component styles*
with our components enabling a more modular design than regular stylesheets.
In this chapter we learn how to load and apply these *component styles*.
## Table Of Contents
* [Using Component Styles](#using-component-styles)
* [Special selectors](#special-selectors)
* [Loading Styles into Components](#loading-styles)
* [Controlling View Encapsulation: Emulated, Native, and None](#view-encapsulation)
* [Appendix 1: Inspecting the generated runtime component styles](#inspect-generated-css)
* [Appendix 2: Loading Styles with Relative URLs](#relative-urls)
Run the of the code shown in this chapter.
## Using Component Styles
For every Angular component we write, we 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 we 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 we give it one string as in this example:
{@example 'component-styles/ts/src/app/hero-app.component.ts'}
Component styles differ from traditional, global styles in a couple of ways.
Firstly, the selectors we put into a component's styles *only apply within the template
of that component*. The `h1` selector in the example above only applies to the `` tag
in the template of `HeroAppComponent`. Any `` elements elsewhere in
the application are unaffected.
This is a big improvement in modularity compared to how CSS traditionally works:
1. We can use the CSS class names and selectors that make the most sense in the context of each component.
1. Class names and selectors are local to the component and won't collide with
classes and selectors used elsewhere in the application.
1. Our component's styles *cannot* be changed by changes to styles elsewhere in the application.
1. We 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.
1. We can change or remove component CSS code in the future without trawling through the
whole application to see where else it may have been used. We just look at the component we're in.
{@a special-selectors}
## Special selectors
Component styles have a few special *selectors* from the world of
[shadow DOM style scoping](https://www.w3.org/TR/css-scoping-1):
### :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):
{@example 'component-styles/ts/src/app/hero-details.component.css' region='host'}
This is the *only* way we can target the host element. We cannot reach
it from inside the component with other selectors, because it is not part of the
component's own template. It is in a parent component's template.
Use the *function form* to apply host styles conditionally by
including another selector inside parentheses after `:host`.
In the next example we target the host element again, but only when it also has the `active` CSS class.
{@example 'component-styles/ts/src/app/hero-details.component.css' region='hostfunction'}
### :host-context
Sometimes it is useful to apply styles based on some condition *outside* a component's view.
For example, there may be a CSS theme class applied to the document `` element, and
we want to change how our component looks based on that.
Use the `:host-context()` pseudo-class selector. It works just like the function
form of `:host()`. It looks for a CSS class in *any ancestor* of the component host element, all the way
up to the document root. It's useful when combined with another selector.
In the following example, we apply a `background-color` style to all `` elements *inside* the component, only
if some ancestor element has the CSS class `theme-light`.
{@example 'component-styles/ts/src/app/hero-details.component.css' region='hostcontext'}
### /deep/
Component styles normally apply only to the HTML in the component's own template.
We can use the `/deep/` selector to force a style down through the child component tree into all the child component views.
The `/deep/` selector works to any depth of nested components, and it applies *both to the view
children and the content children* of the component.
In this example, we target all `` elements, from the host element down
through this component to all of its child elements in the DOM:
{@example 'component-styles/ts/src/app/hero-details.component.css' region='deep'}
The `/deep/` selector also has the alias `>>>`. We can use either of the two interchangeably.
~~~ {.alert.is-important}
The `/deep/` and `>>>` selectors should only be used with **emulated** view encapsulation.
This is the default and it is what we use most of the time. See the
[Controlling View Encapsulation](#view-encapsulation)
section for more details.
~~~
{@a loading-styles}
## Loading Styles into Components
We have several ways to add styles to a component:
* inline in the template HTML
* by setting `styles` or `styleUrls` metadata
* with CSS imports
The scoping rules outlined above apply to each of these loading patterns.
### Styles in Metadata
We can add a `styles` #{_array} property to the `@Component` #{_decorator}.
Each string in the #{_array} (usually just one string) defines the CSS.
{@example 'component-styles/ts/src/app/hero-app.component.ts'}
### Template Inline Styles
We can embed styles directly into the HTML template by putting them
inside `