.row.is-flex {
    display: flex;
    flex-wrap: wrap;
}

.row.is-flex>[class*='col-'] {
    display: flex;
    flex-direction: column;
}


/*
* And with max cross-browser enabled.
* Nobody should ever write this by hand. 
* Use a preprocesser with autoprefixing.
*/

.row.is-flex {
    display: -webkit-box;
    display: -webkit-flex;
    display: -ms-flexbox;
    display: flex;
    -webkit-flex-wrap: wrap;
    -ms-flex-wrap: wrap;
    flex-wrap: wrap;
}

.row.is-flex>[class*='col-'] {
    display: -webkit-box;
    display: -webkit-flex;
    display: -ms-flexbox;
    display: flex;
    -webkit-box-orient: vertical;
    -webkit-box-direction: normal;
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
}