linear-gradient グラデーション http://www.webcreatorbox.com/tech/css-gradient/
background: linear-gradient(to right, rgba($c_mg6,1) 0%, rgba($c_mg1,1) calc(100% / 6), rgba($c_mg2,1) calc(100% / 6 *2), rgba($c_mg3,1) calc(100% / 6 *3), rgba($c_mg4,1) calc(100% / 6 *4), rgba($c_mg5,1) calc(100% / 6 *5),rgba($c_mg6,1) 100%);
body {
background: linear-gradient(-135deg, #E4A972, #9941D8);
}