A CSS Flexbox layout demonstrates responsive box arrangement using the Flexbox model. Six numbered black boxes with white text are centered within a bordered container, wrapping onto multiple lines with a one-rem gap between them. The code uses `display: flex`, `justify-content`, `align-items`, `flex-flow`, and `align-content` properties to control alignment and wrapping. It imports the Roboto font from Google Fonts and applies a plain HTML structure with no JavaScript or external data sources.