关于几个CSS样式不是很清楚

background-position: 0 0, 30px 30px;

 background-image: linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480), linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);

这两个样式怎么理解呀 background-position:0 0,30px 30px 这个参数 没看明白，麻烦帮忙解释一下，谢谢啊