.flex {
    display:flex;
    flow-direction: row;
}

.flex-auto {
    flex:auto
}

.flex-first {
  flex: 0 0;
}

.flex-even {
  flex-grow: 1;
  flex-shrink: 1;
}

.flex-wrap {
    flex-wrap:wrap
}

.book-columns {
    margin-left: -1rem;
    margin-right:-1rem
}

.book-columns > div {
    margin: 1rem 0;
    /* min-width: 10rem; */
    padding:0 1rem
}