要使用CSS淡入工具提示文本，您可以尝试运行以下代码：
<!DOCTYPE html>
<html>
<style>
.mytooltip .mytext {
visibility: hidden;
width: 140px;
background-color: blue;
color: #fff;
z-index: 1;
top: -5px;
right: 110%;
text-align: center;
border-radius: 6px;
padding: 5px 0;
position: absolute;
opacity: 0;
transition: opacity 1s;
}
.mytooltip {
position: relative;
display: inline-block;
margin-left: 150px;
}
.mytooltip .mytext:after {
content: "";
position: absolute;
top: 50%;
left: 100%;
margin-top: -5px;
border-width: 6px;
border-style: solid;
border-color: transparent transparent transparent blue;
}
.mytooltip:hover .mytext {
visibility: visible;
opacity: 1;
}
</style>
<body>
<div class = "mytooltip">Keep mouse cursor over me
<span class = "mytext"> My Tooltip text</span>
</div>
</body>
</html>