<!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 {
width: 200px;
height: 200px;
display: inline-block;
}
.box1 {
background-color: red;
margin-left:-6px;
margin-top: 0px;
}
.box2 {
background-color: green;
line-height:-10px;
}
.box3 {
background-color: blue;
margin-top:0px;
}
</style>
</head>
<body style="margin-top:0px;">
<div class="box1">
<ul>颜色种类
<li>红色</li>
<li>绿色</li>
<li>黄色</li>
</ul>
</div>
<div class="box2">盒子2</div>
<div class="box3">盒子3</div>
</body>
</html>
div {
width: 200px;
height: 200px;
float:left;
}
将display: inline-block;改成float:left;