popup.html

<style>
  :root {
    --background: #fff;
    --text: #272727;
    --hover: #c8c8c9;
    --separator: #d9d9d9;
  }

  @media (prefers-color-scheme: dark) {
    :root {
      --background: #292a2d;
      --text: #eeeeee;
      --hover: #4b4c4f;
      --separator: #383b3e;
    }
  }

  html {
    margin: 0;
    padding: 0;
    background: var(--background);
  }
  body {
    margin: 0;
    padding: 6px 0;
  }
  button {
    font: 13px/16px BlinkMacSystemFont, -apple-system, sans-serif;
    border: none;
    background: transparent;
    white-space: nowrap;
    padding: 6px 12px;
    width: 100%;
    box-sizing: border-box;
    color: var(--text);
    text-align: left;
    display: flex;
    outline: none;
  }
  button:hover {
    background: var(--hover);
  }
  hr {
    border: none;
    border-top: 1px solid var(--separator);
  }
  .shortcut {
    margin-left: auto;
    padding-left: 16px;
  }
</style>

<button id="copy-tab">
  Copy Tab
  <span class="shortcut">Alt+C</span>
</button>
<button id="copy-and-close-tab">
  Copy & Close Tab
  <span class="shortcut">Alt+W</span>
</button>
<hr />
<button id="copy-all-tabs">
  Copy All Tabs
  <span class="shortcut">Alt+Shift+C</span>
</button>
<button id="copy-and-close-all-tabs">
  Copy & Close All Tabs
  <span class="shortcut">Alt+Shift+W</span>
</button>
<hr />
<button id="download-tabs-as-txt">
  Download List of Tabs as Text
</button>
<button id="download-tabs-as-md">
  Download List of Tabs as Markdown
</button>
<button id="download-tabs-as-html">
  Download List of Tabs as HTML
</button>

<script src="lib.js"></script>
<script src="popup.js"></script>