Key statement:
word-wrap:break-word;
word-break:break-all;
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>换行</title>
</head>
<style>
.box1{
width: 200px;
border:1px solid red;
font-size: 18px;
word-wrap:break-word;
word-break:break-all;
}
</style>
<body>
<div class="box1">我是一行很长额文字hello goto 192321245956588654868 lalallaallalallaall</div>
</body>
</html>