为什么.box1后面输入的width:100px没有生效？
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>flex布局</title>
<style type="text/css">
.box {
background: blue;
display: flex;
}
.box div {
width: 200px;
height: 200px;
}
.box1 {
width:100px;
background: red;
}
.box2 {
background: orange;
}
.box3 {
background: green;
}
</style>
</head>
<body>
<div class="box">
<div class="box1"></div>
<div class="box2"></div>
<div class="box3"></div>
</div>
</body>
</html>
看图！！