// flex grid system
.flex-box
    list-style none
    display flex
    flex-wrap wrap
    // border 2px solid red
    .flex-box-1
        flex 1
        // border 2px solid green
    .flex-box-2
        flex 2
    .flex-box-3
        flex 3
    .flex-box-4
        flex 4
.flex-col
    flex-direction column
.justify-content-around
    justify-content space-around
.justify-content-between
    justify-content space-between
.justify-content-start
    justify-content flex-start