Beautiful content starts here.
Foremost, Bootstrap provides a consistent, uniform appearance and design. With very little effort, Bootstrap can be used to transform a hodge-podge site into a professional, visually appealing design.
Sites created with Bootstrap are designed to look & function well on any device including desktops, laptops, tablets and smartphones. Bootstrap is "mobile-first" which means the design for smaller mobile devices is considered foremost.
These are built-in styles for HTML elements such as Buttons, fonts, colors, badges, typography, progress bars, alerts, etc… Using any of these Bootstrap Components is very easy. It’s just a matter of referencing the appropriate Bootstrap CSS class in the HTML markup.
The Bootstrap Grid
Layout helpers using “rows” and “columns”. The Bootstrap Grid System is used for layout, specifically Responsive Layouts. Understanding how it works is vital to understanding Bootstrap. The Grid is made up of groupings of Rows & Columns inside 1 or more Containers.
You may want to customize Bootstrap for several reasons. You may want to change some aspect of the look or styles such as colors, fonts, or borders. You may want to change some aspect of the responsive layout like grid breakpoints or gutter widths. Additionally, you may want to extend Bootstrap classes with new custom classes (ie; btn-custom).
Of course customization is important since not everyone wants that overly recognizable Bootstrap look. Using the methods (CSS or SASS) described it’s fairly easy to transform your Bootstrap 4 sites with a unique look. Once you understand the basic of customization you're on the way to creating custom Bootstrap themes.