When creating my WordPress Theme ShprinkOne I discovered a responsive CSS problem. Resizing the browser reacted as expected on Desktop but not on mobile devices(Phone, Tablet).

As it is well explain on Bootstrap documentation a proper meta tag is needed to turn the responsive CSS behavior on mobile devices. The viewport meta can be used to control how HTML content will appear in mobile devices. It contains a comma-separated list of properties in the form name=value

If it is happening to you, you will have to insert the following meta on your page header to fix the problem for good.

<meta name="viewport" content="width=device-width, initial-scale=1.0">

Sources