bootstrap media queries.

bootstrap-breakpoints.txt

On the Bootstrap 3 media queries documentation it says:

We use the following media queries in our Less files to create the key breakpoints in our grid system.

Extra small devices (phones, less than 768px): No media query since this is the default in Bootstrap

Small devices (tablets, 768px and up): @media (min-width: @screen-sm-min) { ... }

Medium devices (desktops, 992px and up): @media (min-width: @screen-md-min) { ... }

Large devices (large desktops, 1200px and up): @media (min-width: @screen-lg-min) { ... }

https://stackoverflow.com/questions/19592968/bootstrap-3-breakpoints-and-media-queries