Css怎么改变背景图片大小？

Question

比如这个图片的大小是400×400，我要改成200×200。

Answer 1

background-size:200px 200px;

Answer 2

background-size:200px 200px;
background-repeat:no-repeat;

Answer 3

background-image:url('图片地址');
background-size:200px 200px;
background-position:center;

Answer 4

background:url('图片连接') no-repeat;
background-size:200px;