linear-gradient
linear-gradient() 函数用于创建一个表示两种或多种颜色线性渐变的图片。其结果属于gradient数据类型，是一种特别的image数据类型。
/* 渐变轴为45度，从蓝色渐变到红色 */
linear-gradient(45deg, blue, red);
/* 从右下到左上、从蓝色渐变到红色 */
linear-gradient(to left top, blue, red);
/* 从下到上，从蓝色开始渐变、到高度40%位置是绿色渐变开始、最后以红色结束 */
linear-gradient(0deg, blue, green 40%, red)
background: linear-gradient(#e66465, #9198e5);
background: linear-gradient(0.25turn, #3f87a6, #ebf8e1, #f69d3c);
background: linear-gradient(to left, #333, #333 50%, #eee 75%, #333 75%);
background: linear-gradient(217deg, rgba(255,0,0,.8), rgba(255,0,0,0) 70.71%),
linear-gradient(127deg, rgba(0,255,0,.8), rgba(0,255,0,0) 70.71%),
linear-gradient(336deg, rgba(0,0,255,.8), rgba(0,0,255,0) 70.71%);