html5模拟wifi信号图

<style>
    .rss {margin-left:3em; border-radius: 100%; background: #000; width: 0.8em; height: 0.8em; position: relative; }
      .rss::before, .rss::after { border-radius: 100%; position: absolute; content: ""; border-width: .5em; border-style: solid; border-color: #000 transparent transparent; }
      .rss::before { top: -1em; left: -1.1em; width: 2em; height: 2em; }
      .rss::after { top: -2em; left: -2.1em; width: 4em; height: 4em; }
  </style>
  <div class="rss"></div>