css 线性渐变

线性渐变 - 从上到下（默认情况下）

background: linear-gradient(yellow 0%, #fff 100%);

线性渐变 - 从左到右（to right）/从右到左(to left)

background-image: linear-gradient(to right, red , yellow);

对角 - 左上角到右上角

background-image: linear-gradient(to right top, red , yellow);

径向渐变

background-image: radial-gradient(red, yellow, green);

参考：https://www.runoob.com/css3/css3-gradients.html
https://www.jianshu.com/p/c800b12bdba4