<p>Grid classes apply to devices with screen widths greater than or equal to the breakpoint sizes, and override grid classes targeted at smaller devices. Therefore, applying any <code>.col-md-</code> class to an element will not only affect its styling on medium devices but also on large devices if a <code>.col-lg-</code> class is not present.</p>
<p>Using a single set of <code>.col-md-*</code> grid classes, you can create a basic grid system that starts out stacked on mobile devices and tablet devices (the extra small to small range) before becoming horizontal on desktop (medium) devices.</p>