ant-design/.dumi/theme/common/styles/BrowserMockup.tsx

import { css, Global } from '@emotion/react';
import React from 'react';

export default () => (
  <Global
    styles={css`
      /* Browser mockup code
 * Contribute: https://gist.github.com/jarthod/8719db9fef8deb937f4f
 * Live example: https://updown.io
 */

      .browser-mockup {
        position: relative;
        border-top: 2em solid rgba(230, 230, 230, 0.7);
        border-radius: 3px 3px 0 0;
        box-shadow: 0 0.1em 0.5em 0 rgba(0, 0, 0, 0.28);
      }

      .browser-mockup::before {
        position: absolute;
        top: -1.25em;
        left: 1em;
        display: block;
        width: 0.5em;
        height: 0.5em;
        background-color: #f44;
        border-radius: 50%;
        box-shadow: 0 0 0 2px #f44, 1.5em 0 0 2px #9b3, 3em 0 0 2px #fb5;
        content: '';
      }

      .browser-mockup.with-tab::after {
        position: absolute;
        top: -2em;
        left: 5.5em;
        display: block;
        width: 20%;
        height: 0;
        border-right: 0.8em solid transparent;
        border-bottom: 2em solid white;
        border-left: 0.8em solid transparent;
        content: '';
      }

      .browser-mockup.with-url::after {
        position: absolute;
        top: -1.6em;
        left: 5.5em;
        display: block;
        width: ~'calc(100% - 6em)';
        height: 1.2em;
        background-color: white;
        border-radius: 2px;
        content: '';
      }

      .browser-mockup > * {
        display: block;
      }
    `}
  />
);