angular/adev/shared-docs/styles/docs/_callout.scss

// Callout

@mixin docs-callout() {
  .docs-callout {
    // Default theme is purple to blue
    --callout-theme: var(--purple-to-blue-horizontal-gradient);
    border-width: 0;
    border-block-start-width: 2px;
    border-block-end-width: 1px;
    border-style: solid;
    margin-block: 1.5rem;
    border-image: var(--callout-theme) 1;

    // Removes bottom line if followed by another callout
    // Prevents too many lines/visual noise
    &:has(+ .docs-callout) {
      border-block-end-width: 0;
    }

    &::before {
      font-family: var(--icons);
      // content: icon is defined in each docs-alert class below...
      float: right;
      margin-top: 1.35rem;
      color: var(--alert-accent);
      font-size: 1.3rem;
    }

    // Callout heading
    h2,
    h3,
    h4,
    h5,
    h6 {
      background-image: var(--callout-theme);
      background-clip: text;
      -webkit-background-clip: text;
      color: transparent;
      max-width: fit-content;
    }
  }

  .docs-viewer .docs-callout h3 {
    font-size: 0.875rem;
    margin-block: 1.6rem;
  }

  .docs-callout-helpful {
    --callout-theme: var(--purple-to-blue-horizontal-gradient);

    &::before {
      content: 'check_circle';
      color: var(--bright-blue);
    }
  }

  .docs-callout-critical {
    --callout-theme: var(--red-to-orange-horizontal-gradient);

    &::before {
      content: 'warning';
      color: var(--orange-red);
    }
  }

  .docs-callout-important {
    --callout-theme: var(--pink-to-purple-horizontal-gradient);

    &::before {
      content: 'priority_high';
      color: var(--electric-violet);
    }
  }
}