21 - 通用属性 - background-image:#色号50; - 背景+渐变色

background-image

可以用：
background-origin
background-position
background-repeat
background-size
background-attachment
控制

渐变 - 线性 - linear-gradient(上色,下色)

background-image: linear-gradient(#e66465, #9198e5);

渐变 - 线性 - linear-gradient(to right,左色,右色)

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

渐变 - 线性 - linear-gradient(to bottom right,左上色,右下色)

background-image: linear-gradient(to bottom right,#e66465, #9198e5);

渐变 - 角度 - linear-gradient(-90deg,#e66465, #9198e5);

background-image: linear-gradient(-90deg,#e66465, #9198e5);