chromium/chrome/browser/resources/extensions/drop_overlay.html

<style include="cr-hidden-style">
  :host {
    align-items: center;
    background-color: rgba(241, 241, 241, .9);
    color: var(--cr-secondary-text-color);
    display: flex;
    height: 100%;
    justify-content: center;
    position: absolute;
    width: 100%;
    z-index: 10;
  }

  @media (prefers-color-scheme: dark) {
    :host {
      /* TODO(dbeam): share with cr-dialog dialog::backdrop? */
      background-color: rgba(0, 0, 0, .6);
    }
  }

  #container {
    align-items: center;
    display: flex;
    flex-direction: column;
  }

  iron-icon {
    height: 64px;
    margin-bottom: 16px;
    width: 64px;
  }

  #text {
    color: #6e6e6e;
    font-size: 123.1%;
    font-weight: 500;
  }
</style>
<div id="container">
  <iron-icon icon="cr:extension"></iron-icon>
  <div id="text">$i18n{dropToInstall}</div>
</div>