Most web pages are written in a combination of HTML (Hypertext Markup Language) and CSS (Cascading Style Sheets). In short, HTML specifies the content and logical structure of the page, while the CSS specifies how it looks: its colors, fonts, formatting, layout, and styling

CSS flex-box layout is a particular way to specify the layout of HTML pages

One of the most defining features of the flex layout is its ability to form-fit, based on its viewing environment. Flex boxes can adjust in size - either decreasing, to avoid unnecessarily monopolizing space, or increasing to make room for contents to be constrained within its boundaries

Flexbox is another technology worth familiarizing yourself with. Many modern CSS frameworks, notably Bootstrap, incorporate it into their design

Click each panel to see Flexbox (along with a little JavaScript) in action. Double-clicking will reset the page