Change default expansion panel arrow colour for angular material

Question

I have an angular expansion panel as shown below. How can i change the color of the arrow below to white?

My code (HTML):

<md-expansion-panel>
  <md-expansion-panel-header>
    <md-panel-title>
      Personal data
    </md-panel-title>
    <md-panel-description>
      Type your name and age
    </md-panel-description>
  </md-expansion-panel-header>

  <md-form-field>
    <input mdInput placeholder="First name">
  </md-form-field>

  <md-form-field>
    <input mdInput placeholder="Age">
  </md-form-field>
</md-expansion-panel>

My code (TS):

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

/**
 * @title Basic expansion panel
 */
@Component({
  selector: 'expansion-overview-example',
  templateUrl: 'expansion-overview-example.html',
})
export class ExpansionOverviewExample {}

Answer 1

Working code is below:

<md-expansion-panel>
  <md-expansion-panel-header class="specific-class">
    <md-panel-title>
      Personal data
    </md-panel-title>
    <md-panel-description>
      Type your name and age
    </md-panel-description>
  </md-expansion-panel-header>

  <md-form-field>
    <input mdInput placeholder="First name">
  </md-form-field>

  <md-form-field>
    <input mdInput placeholder="Age">
  </md-form-field>
</md-expansion-panel>

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

/**
 * @title Basic expansion panel
 */
@Component({
  selector: 'expansion-overview-example',
  templateUrl: 'expansion-overview-example.html',
  styles: [`
    ::ng-deep .specific-class > .mat-expansion-indicator:after {
      color: white;
    }
  `],
})
export class ExpansionOverviewExample {}

Explanation:

1. In order to style nested elements dynamically added by Angular Material component you need to use special selector ::ng-deep. That allows to work around view encapsulation.

2. In order to override built-in component styles applied dynamically you need to increase CSS specificity for your selector. That's the reason for adding additional CSS class specific-class. If you gonna use selector ::ng-deep .mat-expansion-indicator:after expansion component will override it.