粉红色框是div的高度，文字换行后，溢出也会显示。没有做溢出
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div{
white-space: normal;
word-break: break-all;
word-wrap: break-word;
}
</style>
</head>
<body>
<div style="height: 100px">
<div style="width: 100px;border: 3px solid pink;height: 100px">
I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii I am a doibiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
</div>
</div>
</body>
</html>