侧边栏菜单渐变色 #

.is-active {
    background-image: -webkit-linear-gradient(right, rgba(29,65, 81, 0) 0%, rgba(29,65, 81, 1) 100%);
    span {
        color: #fff;
    }

    &::before {
        width: 4px;
        background-color: #39bab6;
        position: absolute;
        top: 0;
        left: 0;
        bottom: 0;
        content: "";
    }
}