渐变的用法

1）线性渐变
background-image: linear-gradient(direction, color-stop1, color-stop2, ...);

  方向( to right )(to right top)   使用角度单位deg

      颜色1                颜色2

2)径向渐变

语法：background-image: radial-gradient(shape size at position, start-color, ..., last-color);