1. 轮廓
1. 背景：background
background-color background-image background-repeat background-attachment background-position
简写：
background: #ffffff url("tree.png") no-repeat right top;
2. 边框：border
border-style 必须 border-color border-width
border-radius 属性用于向元素添加圆角边框
简写：固定顺序
border: 5px solid red;
3. 外边距：margin
margin: 25px 50px 75px 100px;
原文：https://www.cnblogs.com/JackShi/p/14607213.html