Bootstrap's grid system is arguably its most impressive and most commonly used feature. Therefore, mastering it is essential for any Bootstrap developer as the grid system removes many of the pain-points associated with page layouts, especially responsive page layouts. The grid system solves issues such as the horizontal and vertical positioning of a page's contents and the structure of the page across multiple display widths.
As already noted in Chapter 1, Revving up Bootstrap, Bootstrap 4 is mobile-first. As such, it should come as no surprise that the grid system is optimized for smaller viewports and scales up to suit larger viewports, as opposed to scaling down to smaller viewports.
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What is a viewport?
A viewport is the available display size to render the contents of a page. For example, the size of your browser window, minus the toolbars, scrollbars, and so on, on your display is your viewport. As already noted in Chapter 1 , Revving Up Bootstrap, mobile devices...