Spectre: Getting column to collapse at <600px

[tomcam]

I have a 3 column format where I want the rightmost column to become a row at <= 600px wide. Can't figure it out. Am trying stuff like this to no avail:

@media (max-width: 600px) {
    .container {
        display: flex;
        flex-flow: column;
    }
}

The offending file is at GitHub Source, Preview

Bonus points for anyone who can tell me why bluerobot.svg doesn't display.

[tomcam]

Remove irrelevant debug line

[picturepan2]

@tomcam

<div class="columns">
   <div class="column col-4 col-sm-6"></div>
   <div class="column col-4 col-sm-6"></div>
   <div class="column col-4 col-sm-12"></div>
</div>

[tomcam]

Oh my goodness. Worked perfectly. Thank you.

[picturepan2]

@tomcam You're welcome.