Setting (bootstrap) col width's with media queries

Question

I have a page with a banner and 3 columns, and I am trying to make it so that when the screen width gets too small, that the first 2 columns change from 1/3rd width to 50% width and the last column width change to 100% so that it's below the first two.

When I do this, the height of the columns does change (they change to 50%, considering the columns will now fit underneath each other inside a 100% row), but the width does not. How could I fix this? Thanks in advance!

Codepen

HTML

<section class="section">
  <div class="container-fluid">
    <div class="aboutBanner"> </div>

    <div class="row">
      <div class="col">

      </div>
      <div class="col">

      </div>
      <div class="col">

      </div>
    </div>
  </div>
</section>

related CSS

.aboutBanner {
    height: 30%;
    border: 1px solid blue;
}

.row {
    height: 70%;
}

.row .col {
    height: 100%;
    border: 1px solid red;
}

@media screen and (max-width: 768px){
    .row .col:nth-of-type(1),
    .row .col:nth-of-type(2) {
        height: 50%;
        width: 50%;
    }
    .row .col:nth-of-type(3) {
        height: 50%;
        width: 100%;
        border-style: dashed;
    }
}

Answer 1

Use the Bootstrap responsive grid columns...

https://codepen.io/anon/pen/eMzRyb

<section class="section">
  <div class="container-fluid">
    <div class="aboutBanner">

    </div>
    <div class="row">
      <div class="col-sm-4 col-6">

      </div>
      <div class="col-sm-4 col-6">

      </div>
      <div class="col-sm-4 col-12">

      </div>
    </div>
  </div>
</section>

To visualize this in your codepen I changed the CSS...

.row {
    height: 70%;
}

.row > div {
    border: 1px solid red;
}

Also see: What is the difference among col-lg-*, col-md-* and col-sm-* in Bootstrap?