It is very flexible and easy to use, even for people with little or no CSS experience.
The New Layout System: Fluid Grids
Bootstrap 4 introduces a new responsive grid system that uses percentages instead of pixels to define column widths. This allows columns to be sized relative to their parent element, so you can easily create multi-column layouts without having to do any math yourself. The old 12-column grid from previous versions has been replaced by five tiers of grids: xs , sm , md , lg , and xl
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