css实现鼠标触碰时显示提示框，鼠标移开时隐藏提示框
解决方法：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style>
.modal-title .icon-mutex {
font-size: 16px;
color: #2bb7c5;
text-align: center;
line-height: 20px;
cursor: pointer;
position: relative;
display: inline-block;
width: 20px;
height: 20px;
position: relative;
border: 1px solid #2bb7c5;
border-radius: 50%;
margin-left: 10px;
}
.modal-title .icon-mutex:hover {
color: #2bb7c5;
}
.modal-title i {
width: 250px;
display: none;
position: absolute;
left: -19px;
top: 27px;
font-size: 12px;
font-style:normal;
color: #fff;
text-align: left;
background-color: rgba(1,1,1,0.7);
padding: 3px 5px;
z-index: 2;
}
.modal-title .icon-mutex:hover i {
display: block;
}
.modal-title i::before {
display: inline-block;
width: 0;
height: 0;
content: '';
margin-left: 2px;
vertical-align: middle;
border-bottom: 6px solid #010101b3;
border-right: 6px solid transparent;
border-left: 6px solid transparent;
position: absolute;
top: -5px;
left: 20px;
}
</style>
</head>
<body>
<span class="modal-title" >
<a class="icon-mutex">?<i class="mutex-tip">提示内容：这里是提示框！</i></a>
</span>
</body>
</html>