Stacked inputs with rows using flexbox
The following is my opinion on how to improve your code.


You don't need write flex-flow: row-wrap because flex by default set row, then you can use another property of css flex-wrap: wrap.
If you want to use flex in the whole of your code, you can set flex properties for .row class.
Care about responsiveness, because flex is very good for making your page responsive. Due to this, we use flex-wrap and min-width to our input.




.stacked-inputs,.stacked-inputs .row {
    display: -ms-flexbox;
    display: flex;
    -ms-flex-wrap: wrap;
    flex-wrap: wrap;

}
.stacked-inputs .row {
    display: flex;
    flex-grow: 1;
    flex-shrink: 1;
    flex-basis: 100%;
    margin-bottom: 10px;
}
.stacked-inputs &gt; input,
.stacked-inputs .row &gt; input {
    -ms-flex: 1 1 0%;
    flex: 1 1 0%;
    min-width: 200px;
}