<div class="test" style="text-overflow:ellipsis;">This is some long text that will not fit in the box</div>
<!DOCTYPE html>
<html>
<head>
<style>
div.test
{
white-space:nowrap;
width:12em;
overflow:hidden;
border:1px solid #000000;
}
div.test:hover
text-overflow:inherit;
overflow:visible;
</style>
</head>
<body>
<p>如果您把光标移动到下面两个 div 上，就能够看到全部文本。</p>