* {
    padding: 0;
    margin: 0;
}

html, body {
    width: 100%;
    height: 100%;
}

.col {
    display: flex;
    flex-flow: column wrap-reverse;
    justify-content: center;
    align-items: center;
    flex: 1 1 100px;

}

.row {
    display: flex;
    flex-flow: row wrap-reverse;
    justify-content: center;
    align-items: center;
    flex: 1 1 200px;
}

button {
    height: 50px;
    width: 200px;
    margin: 5px 10px 5px;
}

tr {
    margin: 2px 0 2px;
}

button.sel {
    background-color: lightgreen;
}