app/node_modules/@angular/material/form-field/_form-field-native-select.scss

@use 'sass:math';
@use '../core/tokens/m2/mat/form-field' as tokens-mat-form-field;
@use '../core/tokens/token-utils';

// Width of the Material Design form-field select arrow.
$mat-form-field-select-arrow-width: 10px;
// Height of the Material Design form-field select arrow.
$mat-form-field-select-arrow-height: 5px;
// Horizontal padding that needs to be applied to the native select in a form-field so
// that the absolute positioned arrow does not overlap the select content.
$mat-form-field-select-horizontal-end-padding: $mat-form-field-select-arrow-width + 5px;

$_tokens: tokens-mat-form-field.$prefix, tokens-mat-form-field.get-token-slots();

// Mixin that creates styles for native select controls in a form-field.
@mixin private-form-field-native-select() {
  // Remove the native select down arrow and ensure that the native appearance
  // does not conflict with the form-field. e.g. Focus indication of the native
  // select is undesired since we handle focus as part of the form-field.
  select.mat-mdc-form-field-input-control {
    -moz-appearance: none;
    -webkit-appearance: none;
    background-color: transparent;
    display: inline-flex;
    box-sizing: border-box;

    // By default the cursor does not change when hovering over a select. We want to
    // change this for non-disabled select elements so that it's more obvious that the
    // control can be clicked.
    &:not(:disabled) {
      cursor: pointer;
    }

    &:not(.mat-mdc-native-select-inline) {
      @include token-utils.use-tokens($_tokens...) {
        option {
          @include token-utils.create-token-slot(color, select-option-text-color);
        }

        option:disabled {
          @include token-utils.create-token-slot(color, select-disabled-option-text-color);
        }
      }
    }
  }

  // Native select elements with the `matInput` directive should have Material Design
  // styling. This means that we add an arrow to the form-field that is based on the
  // Material Design specification. We achieve this by adding a pseudo element to the
  // form-field infix.
  .mat-mdc-form-field-type-mat-native-select {
    .mat-mdc-form-field-infix::after {
      content: '';
      width: 0;
      height: 0;
      border-left: math.div($mat-form-field-select-arrow-width, 2) solid transparent;
      border-right: math.div($mat-form-field-select-arrow-width, 2) solid transparent;
      border-top: $mat-form-field-select-arrow-height solid;
      position: absolute;
      right: 0;
      top: 50%;
      margin-top: -#{math.div($mat-form-field-select-arrow-height, 2)};

      // Make the arrow non-clickable so the user can click on the form control under it.
      pointer-events: none;

      @include token-utils.use-tokens($_tokens...) {
        @include token-utils.create-token-slot(color, enabled-select-arrow-color);
      }

      [dir='rtl'] & {
        right: auto;
        left: 0;
      }
    }

    @include token-utils.use-tokens($_tokens...) {
      &.mat-focused .mat-mdc-form-field-infix::after {
        @include token-utils.create-token-slot(color, focus-select-arrow-color);
      }

      &.mat-form-field-disabled .mat-mdc-form-field-infix::after {
        @include token-utils.create-token-slot(color, disabled-select-arrow-color);
      }
    }

    // Add padding on the end of the native select so that the content does not
    // overlap with the Material Design arrow.
    .mat-mdc-form-field-input-control {
      padding-right: $mat-form-field-select-horizontal-end-padding;
      [dir='rtl'] & {
        padding-right: 0;
        padding-left: $mat-form-field-select-horizontal-end-padding;
      }
    }
  }
}