flex-grow not working in column layout

I am trying to have the views-cntnr take up any space not used by views-cntnr and menubar divs. To achieve this, I have a flex display set to column direction. Then I set the flex-grow property for the views-cntnr to 1. Doesn't appear to be doing anything. JSFiddle

NOTE: Not sure if this matters but I have some nested flex displays going on.

HTML

<script src="https://code.jquery.com/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<script src="https://code.jquery.com/jquery-2.1.4.js"></script>
<script src="https://code.jquery.com/jquery-1.11.3.js"></script>
<script src="https://code.jquery.com/ui/1.11.4/jquery-ui.js"></script>

<section class="analysis">
  <div class="menubar">
    <div class="view-ctrls text-center">
      <div class="btn-group" role="group">
        <button class="btn btn-default" ng-class="{'active-view': active_views[0]}" ng-click="toggleView(0)">R-Theta</button>
        <button class="btn btn-default" ng-class="{'active-view': active_views[1]}" ng-click="toggleView(1)">Cartesian</button>
        <button class="btn btn-default" ng-class="{'active-view': active_views[2]}" ng-click="toggleView(2)">Longitudinal</button>
        <button class="btn btn-default" ng-class="{'active-view': active_views[3]}" ng-click="">Console</button>
      </div>
    </div>
  </div>
  <div id="views-cntnr">
    <div class="r1">
      <div id="v1" class="view">V1</div>
      <div id="v2" class="view">V2</div>
      <div id="v3" class="view">V3</div>
    </div>
    <div class="r2">
      <div id="v4" class="view">V4</div>
    </div>
  </div>
  <div id="frame-ctrl-cntnr">
    <div id="frame-num" class="frame-ctrl"># X</div>
    <div id="frame-range-cntnr" class="frame-ctrl">
      <input type="range">
    </div>
  </div>
</section>

CSS

.analysis {
  display: flex;
  flex-direction: column;
}


/* MENUBAR */

.menubar {
  padding: 4px 0 4px;
  background-color: #eee;
}


/* menubar */


/* VIEWS */

#views-cntnr {
  display: flex;
  flex-direction: column;
  flex-grow: 1;
}


/* ROW 1 */

.r1 {
  display: flex;
}

.r1 .view {
  flex-grow: 1;
  border: black 1px solid;
  border-right: none;
}

.r1 .view:last-child {
  border-right: black 1px solid;
}
/* row 1 */

/* ROW 2 */
.r2 .view {
  border: black 1px solid;
  border-top: none;
}


/* row 2 */


/* views */


/* FRAME CTRL */

#frame-ctrl-cntnr {
  display: flex;
}

.frame-ctrl {
  border: black 1px solid;
  border-top: none;
  border-right: none;
}

.frame-ctrl:last-child {
  border-right: black 1px solid;
}

#frame-num {
 width: 50px;
}

#frame-range-cntnr {
  flex-grow: 1;
  padding: 4px;
}

/* frame ctrl */

Everything in your code is working fine.

The only issue is that your flex container has no specified height. Therefore, the height resolves to auto, meaning the height of the content.

The flex-grow property distributes free space in the container. With no free space in your container, flex-grow has nothing to do.

Try this adjustment to your CSS:

.analysis {
    display: flex;
    flex-direction: column;
    height: 100vh;
}

This tells the flex container to be the height of the viewport. Now the height of the container is taller than the height of the content, and you will notice flex-grow doing its work.

Revised Fiddle

Learn more about the height: auto default on most elements.