W3School TIY Editor

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.tooltip {
  position: relative;
  display: inline-block;
}

.tooltip .tooltiptext {
  visibility: hidden;
  width: 140px;
  background-color: #555;
  color: #fff;
  text-align: center;
  border-radius: 6px;
  padding: 5px;
  position: absolute;
  z-index: 1;
  bottom: 150%;
  left: 50%;
  margin-left: -75px;
  opacity: 0;
  transition: opacity 0.3s;
}

.tooltip .tooltiptext::after {
  content: "";
  position: absolute;
  top: 100%;
  left: 50%;
  margin-left: -5px;
  border-width: 5px;
  border-style: solid;
  border-color: #555 transparent transparent transparent;
}

.tooltip:hover .tooltiptext {
  visibility: visible;
  opacity: 1;
}
</style>
</head>
<body>

<p>点击按钮可复制文本框中的文本。之后请尝试将文本（例如使用 ctrl+v）粘贴到另一个窗口中，以查看效果。</p>

<div class="tooltip">
<button onclick="myFunction()" onmouseout="outFunc()">
  <span class="tooltiptext" id="myTooltip">复制到剪贴板</span>
  复制文本
  </button>
</div>

function outFunc() {
  var tooltip = document.getElementById("myTooltip");
  tooltip.innerHTML = "Copy to clipboard";
}
</script>
</body>
</html>