margin拖拽，又叫 margin-top傳遞
父子級(jí)包含的時(shí)候子級(jí)的margin-top會(huì)傳遞給父級(jí)(會(huì)傳給最后一層父級(jí))
解決方案

eg:<div>
          <p></p>
     </div>

1.父級(jí)給padding-top(推薦)

div{ width:400px; height:390px; background:red; padding-top:10px; }
p{ width:200px; height:200px; background:pink; }

2.給父級(jí)加overflow:hidden;子級(jí)加margin-top

div{ width:400px; height:400px; background:red; overflow:hidden; }
p{ width:200px; height:200px; background:pink; margin-top:10px; }

3.給父級(jí)加border:1px solid red;子級(jí)加margin-top

div{ width:398px; height:398px; background:red; border:1px solid #ccc; }
p{ width:200px; height:200px; background:pink; margin-top:10px; }