If you want to test the behavior of your boxes for various viewports and devices then all you need is Google Chrome. Let's see how.
- Open Google Chrome and navigate to the page in which you want to test your box
- Hit the F12 key on your keyboard
- Click the icon as shown in the screenshot above
As shown in the screenshot above you can test the responsiveness of your box for various devices or even your own custom resolution and device orientation.
If you are interested for more details on how to use this tool we encourage you to take a look on the Google Developer's Blog
This tool can only emulate the devices it offers and therefore the results should not be considered as a 100% replication of an actual device's results. If you want to be sure about the behavior of your boxes for various devices then there's no other way than testing on those specific devices.