Can you explain the mechanics behind Angular Component CSS encapsulation?

Is it possible to avoid CSS conflicts when using multiple style sheets?

Consider Style 1:

.heading {
  color: green;
}

And Style 2:

.heading {
  color: blue;
}

If these two styles are applied in different views and rendered on a layout as a Partial View, there could be conflicts where one overrides the other.

However,

With Angular (refer to page 16), how do these styles coexist in different components without being overridden?

For instance:

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

@Component({
 selector: 'app-user-item',
 template: '<p class="heading">abc</p>',
 styleUrls: ['./user-item.css']
})
export class UserItemComponent implements OnInit {

  constructor() {}

  ngOnInit() {}

}

In user-item.css:

.heading{ color :green}

In app-user.component.ts:

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

@Component({
 selector: 'app-user',
 template: '<p class="heading">abc</p>',
 styleUrls: ['./user.css']
})
export class UserItemComponent implements OnInit {

  constructor() {}

  ngOnInit() {}

}

In user.css:

.heading{ color :blue}

When displaying this on a page:

<app-user></app-user>
<app-user-item></app-user-item>

The outcome is similar to this screenshot:

https://i.sstatic.net/9NPUq.png

Answer №1

In Angular, there is default emulation of a shadow DOM.

This means that specific HTML attributes are dynamically created and only apply to elements within that component.

For instance:

<app-user></app-user>
<app-user-item></app-user-item>

will be changed to

<app-user _ngcontent-1></app-user>
<app-user-item _ngcontent-2></app-user-item>

Additionally, your CSS will be modified as follows:

.heading[_ngcontent-1] { color: blue }
.heading[_ngcontent-2] { color: green }

More information can be found here and in the documentation here

Answer №2

One of Angular's convenient features is its built-in CSS encapsulation. By default, when creating a new project, the styles.css file located at the project root applies universally across the application, while component-specific styles in files like foo.component.css are limited to that specific component only. However, Angular provides various methods for encapsulating styles beyond this default behavior. Let's explore some alternative approaches.

@Component({
 selector: 'app-foo',
 templateUrl: './foo.component.html',
 styleUrls: ['./foo.component.css']
})

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