1、首先在项目目录中添加一张图片
3、页面显示结果如下图所示，这是重复平铺背景图片的效果
5、设置为不平铺之后页面显示结果如下图所示
7、页面展示效果如图，因为top = top center = center top = 50% 0%，表示居中的意思
8、关键词的解释如下：top left = left top = 0% 0%top = top center = center top = 50% 0%right top = top right = 100% 0%left = left center = center left = 0% 50%center = center center = 50% 50%right = right center = center right = 100% 50%bottom left = left bottom = 0% 100%bottom = bottom center = center bottom = 50% 100%bottom right = right bottom = 100% 100%
