如何在html/css中更改选项卡窗格颜色？

<div class="tab">
  <button class="tab-link active" onclick="openTab(event,'tab1')">选项卡1</button>
  <button class="tab-link" onclick="openTab(event,'tab2')">选项卡2</button>
</div>

<div id="tab1" class="tab-content">
  <h3>选项卡1的内容</h3>
  <p>这里是选项卡1的内容。</p>
</div>

<div id="tab2" class="tab-content" style="display:none;">
  <h3>选项卡2的内容</h3>
  <p>这里是选项卡2的内容。</p>
</div>

.tab {
  overflow: hidden;
  background-color: #f1f1f1;
}

.tab button {
  background-color: inherit;
  float: left;
  border: none;
  outline: none;
  cursor: pointer;
  padding: 14px 16px;
  transition: 0.3s;
}

.tab button:hover {
  background-color: #ddd;
}

.tab button.active {
  background-color: #ccc;
}

.tab-content {
  display: none;
  padding: 20px;
  background-color: #fff;
}

function openTab(evt, tabName) {
  var i, tabcontent, tablinks;

  tabcontent = document.getElementsByClassName("tab-content");
  for (i = 0; i < tabcontent.length; i++) {
    tabcontent[i].style.display = "none";
  }

  tablinks = document.getElementsByClassName("tab-link");
  for (i = 0; i < tablinks.length; i++) {
    tablinks[i].className = tablinks[i].className.replace(" active", "");
  }

  document.getElementById(tabName).style.display = "block";
  evt.currentTarget.className += " active";
}