chrome/browser/resources/md_extensions/drop_overlay.html

<link rel="import" href="chrome://resources/html/cr.html">
<link rel="import" href="chrome://resources/html/cr/ui/drag_wrapper.html">
<link rel="import" href="chrome://resources/html/load_time_data.html">
<link rel="import" href="chrome://resources/html/polymer.html">
<link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
<link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
<link rel="import" href="chrome://extensions/drag_and_drop_handler.html">

<dom-module id="extensions-drop-overlay">
  <template>
    <style>
      [hidden] {
        display: none !important;
      }

      :host {
        align-items: center;
        background-color: white;
        display: flex;
        height: 100%;
        justify-content: center;
        opacity: 0.5;
        position: absolute;
        width: 100%;
        z-index: 10;
      }

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

      iron-icon {
        color: var(--paper-teal-a400);
        height: 64px;
        width: 64px;
      }
    </style>
    <div id="container">
      <iron-icon icon="extension"></iron-icon>
      <div>$i18n{dropToInstall}</div>
    </div>
  </template>
  <script src="chrome://extensions/drop_overlay.js"></script>
</dom-module>