AngularJS conditional styling

can someone please provide me with the correct AngularJS syntax to swap this one to ng-class:

<div class="visible-md pull-left">
...
</div>

(= if screen size is medium, pull the content of the div to left)

Please note that I have seen this post and went through all the examples but none seemed to the do trick.

<div ng-class="{???}">
...
</div>

Thank you for the help!

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Source Url AngularJS conditional styling