Core concepts

• Breakpoints are the building blocks of responsive design. Use them to control when your layout can be adapted at a particular viewport or device size.
• Use media queries to architect your CSS by breakpoint. Media queries are a feature of CSS that allow you to conditionally apply styles based on a set of browser and operating system parameters. We most commonly use min-width in our media queries.
• Mobile first, responsive design is the goal. Bootstrap’s CSS aims to apply the bare minimum of styles to make a layout work at the smallest breakpoint, and then layers on styles to adjust that design for larger devices. This optimizes your CSS, improves rendering time, and provides a great experience for your visitors.