.flex .m1 {
    padding: 10px;
    margin: 10px;
}

.c6 {
    display: inline-block;
    vertical-align: top;
    box-sizing: border-box;
}

@media all and (max-width: 599px) {
    .flex {
        display: flex;
        flex-wrap: wrap;
    }
}

@media all and (min-width: 600px) {
    .flex {
        display: flex;
        flex-wrap: wrap;
        justify-content: center;
    }
}

@media all and (min-width: 600px) and (max-width: 940px) {
    .c6 { width: 50%; }
}

@media all and (min-width: 800px) and (max-width: 1099px) {
    .c6 { width: 33.3333333%; }
}

@media all and (min-width: 1100px) {
    .c6 { width: 16.666666% }
}