如何从父组件的 CSS 文件中设置子组件的样式？

Question

I've got a parent component:

<parent></parent>

And I want to populate this group with child components:

<parent>
  <child></child>
  <child></child>
  <child></child>
</parent>

Parent template:

<div class="parent">
  <!-- Children goes here -->
  <ng-content></ng-content>
</div>

Child template:

<div class="child">Test</div>

Since parent and child are two separate components, their styles are locked to their own scope.

In my parent component I tried doing:

.parent .child {
  // Styles for child
}

But the .child styles are not getting applied to the child components.

I tried using styleUrls to include the parent 's stylesheet into child component to solve the scope issue:

// child.component.ts
styleUrls: [
  './parent.component.css',
  './child.component.css',
]

But that didn't help, also tried the other way by fetching the child stylesheet into parent but that didn't help either.

So how do you style child components that are included into a parent component?

Answer 1

Update - Newest Way

Don't do it, if you can avoid it. As Devon Sans points out in the comments: This feature will most likely be deprecated.

#Update - Newer Way From Angular 4.3.0 , all piercing css combinators were deprecated. Angular team introduced a new combinator ::ng-deep (still it is experimental and not the full and final way) as shown below,

DEMO : https://plnkr.co/edit/RBJIszu14o4svHLQt563?p=preview

styles: [
    `
     :host { color: red; }
     
     :host ::ng-deep parent {
       color:blue;
     }
     :host ::ng-deep child{
       color:orange;
     }
     :host ::ng-deep child.class1 {
       color:yellow;
     }
     :host ::ng-deep child.class2{
       color:pink;
     }
    `
],



template: `
      Angular2                                //red
      <parent>                                //blue
          <child></child>                     //orange
          <child class="class1"></child>      //yellow
          <child class="class2"></child>      //pink
      </parent>      
    `

---

# Old way

You can use encapsulation mode and/or piercing CSS combinators >>>, /deep/ and ::shadow

working example : http://plnkr.co/edit/1RBDGQ?p=preview

 styles: [ ` :host { color: red; } :host >>> parent { color:blue; } :host >>> child{ color:orange; } :host >>> child.class1 { color:yellow; } :host >>> child.class2{ color:pink; } ` ], template: ` Angular2 //red <parent> //blue <child></child> //orange <child class="class1"></child> //yellow <child class="class2"></child> //pink </parent> `

Answer 2

You should NOT use ::ng-deep , it is deprecated. In Angular, the proper way to change the style of children's component from the parent is to use encapsulation (read the warning below to understand the implications):

import { ViewEncapsulation } from '@angular/core';

@Component({
    ....
    encapsulation: ViewEncapsulation.None
})

And then, you will be able to modify the css form your component without a need from ::ng-deep

.mat-sort-header-container {
  display: flex;
  justify-content: center;
}

WARNING: Doing this will make all css rules you write for this component to be global.

In order to limit the scope of your css to this component and his child only, add a css class to the top tag of your component and put your css "inside" this tag:

template:
    <div class='my-component'>
      <child-component class="first">First</child>
    </div>,

Scss file:

.my-component {
  // All your css goes in there in order not to be global
}

Answer 3

UPDATE 3:

::ng-deep is also deprecated which means you should not do this at all anymore. It is unclear how this affects things where you need to override styles in child components from a parent component. To me it seems odd if this gets removed completely because how would this affect things as libraries where you need to override styles in a library component?

Comment if you have any insight in this.

UPDATE 2:

Since /deep/ and all other shadow piercing selectors are now deprecated. Angular dropped ::ng-deep which should be used instead for a broader compatibility.

UPDATE:

If using Angular-CLI you need to use /deep/ instead of >>> or else it will not work.

ORIGINAL:

After going to Angular2's Github page and doing a random search for "style" I found this question: Angular 2 - innerHTML styling

Which said to use something that was added in 2.0.0-beta.10 , the >>> and ::shadow selectors.

(>>>) (and the equivalent/deep/) and ::shadow were added in 2.0.0-beta.10. They are similar to the shadow DOM CSS combinators (which are deprecated) and only work with encapsulation: ViewEncapsulation.Emulated which is the default in Angular2. They probably also work with ViewEncapsulation.None but are then only ignored because they are not necessary. These combinators are only an intermediate solution until more advanced features for cross-component styling is supported.

So simply doing:

:host >>> .child {}

In parent 's stylesheet file solved the issue. Please note, as stated in the quote above, this solution is only intermediate until more advanced cross-component styling is supported.

Answer 4

Sadly it appears that the /deep/ selector is deprecated (at least in Chrome) https://www.chromestatus.com/features/6750456638341120

In short it appears there is (currently) no long term solution other than to somehow get your child component to style things dynamically.

You could pass a style object to your child and have it applied via:
<div [attr.style]="styleobject">

Or if you have a specific style you can use something like:
<div [style.background-color]="colorvar">

More discussion related to this: https://github.com/angular/angular/issues/6511

Answer 5

有同样的问题，所以如果你将 angular2-cli 与 scss/sass 一起使用，请使用“/deep/”而不是“>>>”，最后一个选择器尚不支持（但与 css 一起使用时效果很好）。

Answer 6

If you want to be more targeted to the actual child component than you should do the follow. This way, if other child components share the same class name, they won't be affected.

Plunker: https://plnkr.co/edit/ooBRp3ROk6fbWPuToytO?p=preview

For example:

import {Component, NgModule } from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>I'm the host parent</h2>
      <child-component class="target1"></child-component><br/>
      <child-component class="target2"></child-component><br/>
      <child-component class="target3"></child-component><br/>
      <child-component class="target4"></child-component><br/>
      <child-component></child-component><br/>
    </div>
  `,
  styles: [`

  /deep/ child-component.target1 .child-box {
      color: red !important; 
      border: 10px solid red !important;
  }  

  /deep/ child-component.target2 .child-box {
      color: purple !important; 
      border: 10px solid purple !important;
  }  

  /deep/ child-component.target3 .child-box {
      color: orange !important; 
      border: 10px solid orange !important;
  }  

  /* this won't work because the target component is spelled incorrectly */
  /deep/ xxxxchild-component.target4 .child-box {
      color: orange !important; 
      border: 10px solid orange !important;
  }  

  /* this will affect any component that has a class name called .child-box */
  /deep/ .child-box {
      color: blue !important; 
      border: 10px solid blue !important;
  }  


  `]
})
export class App {
}

@Component({
  selector: 'child-component',
  template: `
    <div class="child-box">
      Child: This is some text in a box
    </div>
  `,
  styles: [`
    .child-box {
      color: green;    
      border: 1px solid green;
    }
  `]
})
export class ChildComponent {
}


@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App, ChildComponent ],
  bootstrap: [ App ]
})
export class AppModule {}

Hope this helps!

codematrix

Answer 7

You should not write CSS rules for a child component elements in a parent component, since an Angular component is a self-contained entity which should explicitly declare what is available for the outside world. If child layout changes in the future, your styles for that child component elements scattered across other components' SCSS files could easily break, thus making your styling very fragile. That's what ViewEncapsulation is for in the case of CSS. Otherwise, it would be the same if you could assign values to private fields of some class from any other class in Object Oriented Programming.

Therefore, what you should do is to define a set of classes you could apply to the child host element and implement how the child responds to them.

Technically, it could be done as follows:

// child.component.html:
<span class="label-1"></span>

// child.component.scss:
:host.child-color-black {
    .label-1 {
        color: black;
    }
}

:host.child-color-blue {
    .label-1 {
        color: blue ;
    }
}

// parent.component.html:
<child class="child-color-black"></child>
<child class="child-color-blue"></child>

In other words, you use :host pseudo-selector provided by Angular + set of CSS classes to define possible child styles in child component itself. You then have the ability to trigger those styles from outside by applying pre-defined classes to the <child> host element.

Answer 8

Actually there is one more option. Which is rather safe. You can use ViewEncapsulation.None BUT put all your component styles into its tag (aka selector). But anyway always prefer some global style plus encapsulated styles.

Here is modified Denis Rybalka example:

import { Component, ViewEncapsulation } from '@angular/core';

@Component({
  selector: 'parent',
  styles: [`
    parent {
      .first {
        color:blue;
      }
      .second {
        color:red;
      }
    }
 `],
 template: `
    <div>
      <child class="first">First</child>
      <child class="second">Second</child>
    </div>`,
  encapsulation: ViewEncapsulation.None,
})
export class ParentComponent  {
  constructor() { }
}

Answer 9

There are a few options to achieve this in Angular:

1) You can use deep css selectors

:host >>> .childrens {
     color: red;
 }

2) You can also change view encapsulation it's set to Emulated as a default but can be easily changed to Native which uses Shadow DOM native browser implementation, in your case you just need to disable it

For example:`

import { Component, ViewEncapsulation } from '@angular/core';

@Component({
  selector: 'parent',
  styles: [`
    .first {
      color:blue;
    }
    .second {
      color:red;
    }
 `],
 template: `
    <div>
      <child class="first">First</child>
      <child class="second">Second</child>
    </div>`,
  encapsulation: ViewEncapsulation.None,
 })
 export class ParentComponent  {
   constructor() {

   }
 }

Answer 10

I find it a lot cleaner to pass an @INPUT variable if you have access to the child component code:

The idea is that the parent tells the child what its state of appearance should be, and the child decides how to display the state. It's a nice architecture

SCSS Way:

.active {
  ::ng-deep md-list-item {
    background-color: #eee;
  }
}

Better way: - use selected variable:

<md-list>
    <a
            *ngFor="let convo of conversations"
            routerLink="/conversations/{{convo.id}}/messages"
            #rla="routerLinkActive"
            routerLinkActive="active">
        <app-conversation
                [selected]="rla.isActive"
                [convo]="convo"></app-conversation>
    </a>
</md-list>

Answer 11

As of today (Angular 9), Angular uses a Shadow DOM to display the components as custom HTML elements . One elegant way to style those custom elements might be using custom CSS variables . Here is a generic example:

 class ChildElement extends HTMLElement { constructor() { super(); var shadow = this.attachShadow({mode: 'open'}); var wrapper = document.createElement('div'); wrapper.setAttribute('class', 'wrapper'); // Create some CSS to apply to the shadow dom var style = document.createElement('style'); style.textContent = ` /* Here we define the default value for the variable --background-clr */ :host { --background-clr: green; } .wrapper { width: 100px; height: 100px; background-color: var(--background-clr); border: 1px solid red; } `; shadow.appendChild(style); shadow.appendChild(wrapper); } } // Define the new element customElements.define('child-element', ChildElement);

 /* CSS CODE */ /* This element is referred as :host from the point of view of the custom element. Commenting out this CSS will result in the background to be green, as defined in the custom element */ child-element { --background-clr: yellow; }

 <div> <child-element></child-element> </div>

As we can see from the above code, we create a custom element, just like Angular would do for us with every component, and then we override the variable responsible for the background color within the shadow root of the custom element, from the global scope.

In an Angular app, this might be something like:

parent.component.scss

child-element {
  --background-clr: yellow;
}

child-element.component.scss

:host {
  --background-clr: green;
}

.wrapper {
  width: 100px;
  height: 100px;
  background-color: var(--background-clr);
  border: 1px solid red;
}

Answer 12

Since /deep/, >>>, and ::ng-deep are all deprecated. The best approach is to use the following in your child component styling

:host-context(.theme-light) h2 {
  background-color: #eef;
}

This will look for the theme-light in any of the ancestors of your child component. See docs here: https://angular.io/guide/component-styles#host-context

Answer 13

The quick answer is you shouldn't be doing this, at all. It breaks component encapsulation and undermines the benefit you're getting from self-contained components. Consider passing a prop flag to the child component, it can then decide itself how to render differently or apply different CSS, if necessary.

<parent>
  <child [foo]="bar"></child>
</parent>

Angular is deprecating all ways of affecting child styles from parents.

https://angular.io/guide/component-styles#deprecated-deep--and-ng-deep

Answer 14

i also had this problem and didnt wanted to use deprecated solution so i ended up with:

in parrent

 <dynamic-table
  ContainerCustomStyle='width: 400px;'
  >
 </dynamic-Table>

child component

@Input() ContainerCustomStyle: string;

in child in html div

 <div class="container mat-elevation-z8"
 [style]='GetStyle(ContainerCustomStyle)' >

and in code

constructor(private sanitizer: DomSanitizer) {  }

  GetStyle(c) {
    if (isNullOrUndefined(c)) { return null; }
    return  this.sanitizer.bypassSecurityTrustStyle(c);
  }

works like expected and should not be deprecated ;)

Answer 15

For assigning an element's class in a child component you can simply use an @Input string in the child's component and use it as an expression inside the template. Here is an example of something we did to change the icon and button type in a shared Bootstrap loading button component, without affecting how it was already used throughout the codebase:

app-loading-button.component.html (child)

<button class="btn {{additionalClasses}}">...</button>

app-loading-button.component.ts

@Input() additionalClasses: string;

parent.html

<app-loading-button additionalClasses="fa fa-download btn-secondary">...</app-loading-button>

Answer 16

What I prefer to achieve this is the following:

use @Component to add css class to host element and set encapsulation to none. Then reference that class which was added to the host within the components style.css.scss This will allow us to declare styles which will only affect ourselves and our children within scope of our class. fe

@Component({
  selector: 'my-component',
  templateUrl: './my-component.page.html',
  styleUrls: ['./my-component.page.scss'],
  host: {
    class: 'my-component-class'
  },
  encapsulation: ViewEncapsulation.None
})

in combination with the following css (my-component.page.scss)

// refer ourselves so we are allowed to overwrite children but not global styles
.my-component-class {
  // will effect direct h1 nodes within template and all h1 elements within child components of the 
  h1 {
    color: red;
  }
}
// without class "scope" will affect all h1 elements globally
h1 {
  color: blue;
}

Answer 17

As the internet updates I've come across a solution.

First some caveats.

1. Still don't do it. To clarify, I wouldn't plan on child components allowing you to style them. SOC. If you as the component designer want to allow this then all the more power to you.
2. If your child doesn't live in the shadow dom then this won't work for you.
3. If you have to support a browser that can't have a shadow dom then this also won't work for you.

First, mark your child component's encapsulation as shadow so it renders in the actual shadow dom. Second, add the part attribute to the element you wish to allow the parent to style. In your parent's component stylesheet you can use the ::part() method to access

Answer 18

This is a solution with just vanilla css, nothing fancy, you don't even need !important . I assume you can't modify the child, otherwise the answer is even more simple, I put that answer at the end just in case.

Overriding a child's CSS is sometimes needed when using a pre-made component from a library, and the devs have not provided any class input variables. ::ng-deep is deprecated and encapsulation: ViewEncapsulation.None turns all of your component's CSS global. So here is a simple solution that uses neither of those.

The fact is, we do need a global style in order for the CSS to reach the child. So, we can just put the style in styles.css or we can create a new CSS file and add it to the styles array in angular.json . The only issue is that we need a specific selector so as not to target other elements. That's a pretty easy solution - just add a unique class name to the html, I recommend using the parent component's name in the class name to ensure it is unique.

Parent Component

<child class="child-in-parent-component"></child>

Let's pretend we want to change the background-color of all the buttons within the child, we do need to achieve the correct specificity to make sure our styles take precedence. We can do this with !important next to all our properties, but a better way is to just repeat the class name until our selector is specific enough, may take a few tries. That way, someone else can override this css again if necessary.

Global Styles File

.child-in-parent-component.child-in-parent-component.child-in-parent-component
  button {
  background-color: red;
}

or quick and dirty with !important (not recommended)

.child-in-parent-component button {
  background-color: red !important;
}

---

If the child component can be modified

Simply add an input variable to the component and make use of Angular's ngStyle directive. You can add multiple variables to style multiple areas of your component.

Child Component

type klass = { [prop: string]: any } | null;

@Component({...})
export class ChildComponent {
  @Input() containerClass: klass = null;
  @Input() pClass: klass = null;
...
}

<div [ngStyle]="containerClass">
  <p [ngStyle]="pClass">What color will I be?</p>
</div>

Parent Component

<child
  [containerClass]="{ padding: '20px', 'background-color': 'black' }"
  [pClass]="{ color: 'red' }"
>
</child>

This is the intended way to create a component with a dynamic style. Many pre-made components will have a similar input variable.

Answer 19

this has worked for me

in the parent component:

<child-component [styles]="{width: '160px', borderRadius: '16px'}" >
</child-component>

Answer 20

I propose an example to make it more clear, since angular.io/guide/component-styles states:

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.

On app.component.scss , import your *.scss if needed. _colors.scss has some common color values:

$button_ripple_red: #A41E34;
$button_ripple_white_text: #FFF;

Apply a rule to all components

All the buttons having btn-red class will be styled.

@import `./theme/sass/_colors`;

// red background and white text
:host /deep/ button.red-btn {
    color: $button_ripple_white_text;
    background: $button_ripple_red;
}

Apply a rule to a single component

All the buttons having btn-red class on app-login component will be styled.

@import `./theme/sass/_colors`;

/deep/ app-login button.red-btn {
    color: $button_ripple_white_text;
    background: $button_ripple_red;
}

Answer 21

I have solved it outside Angular. I have defined a shared scss that I'm importing to my children.

shared.scss

%cell {
  color: #333333;
  background: #eee;
  font-size: 13px;
  font-weight: 600;
}

child.scss

@import 'styles.scss';
.cell {
  @extend %cell;
}

My proposed approach is a way how to solve the problem the OP has asked about. As mentioned at multiple occasions, ::ng-deep, :ng-host will get depreciated and disabling encapsulation is just too much of a code leakage, in my view.

Answer 22

let 'parent' be the class-name of parent and 'child' be the class-name of child

.parent .child{
//css definition for child inside parent components
} 

you can use this format to define CSS format to 'child' component inside the 'parent'