Line up adjacent DIVs vertically without forced <BR> - html

Question

JSFiddle: https://jsfiddle.net/yL9b2ewu/1/
In this fiddle I have 3 DIVs using Bootstrap 3.3.7 that are next to each other; each DIV is col-sm-3.
Each DIV contains a fixed-size button, then there should be a small amount of space under the button, and then optional explanatory text. Each DIV should end with a border at the same level as the lowest available DIV regardless of whether it has text or not.
One solution is to hard-code some <BR>s for the explanation section. In the 3rd DIV I could put in 4 fixed <BR>s. But this hackery doesn't seem right to me, there should be something dynamic and robust.
<div class="col-md-12 col-sm-12 col-xs-12" style="margin-top:10px; margin-bottom: 10px; font-family:'Source Sans Pro', sans-serif; font-size: 14px">
<div class="col-sm-4 cardstyle">
<button type="button" class="btn btn-success btnSubmitWizard"><b>Submit Recall Now<br><br></b></button>
<br><br>No changes can be made after the recall is submitted.
<!-- Can Insert <BR> here but wrong approach -->
</div>
<div class="col-sm-4 cardstyle">
<button type="button" class="btn btn-primary btnSubmitWizard"><b>Review and Edit<br><br></b></button>
<br><br>Review or edit timeline before submitting.
<!-- Can Insert <BR> here but wrong approach -->
</div>
<div class="col-sm-4 cardstyle">
<button type="button" class="btn btn-primary btnSubmitWizard"><b>Logout and<br>Submit Later </b></button>
<br><br>
<!-- Can Insert <BR> here but wrong approach -->
</div>
</div>

Answer 1

I think that you could select only the last div using :last-child and add to it a bigger padding-bottom.

Answer 2

Give a class for the parent of the columns. Something like .colsParent.
Then, for the same breakpoint of Bootstrap #media, you set flexbox for this element.
#media (min-width: 768px) {
.colsParent {
display: flex;
}
}
By default, it fills the full height of the entire column.
Do not set display: flex inline, because it will affect the layout for devices smaller than the breakpoint above.