The visible area of a web page within the browser window, which varies by device and window size. Viewport dimensions determine breakpoint behavior and affect what's visible without scrolling. The viewport meta tag ensures proper scaling on mobile devices.

A CSS unit equal to 1% of the browser viewport height, enabling layouts relative to screen size. Vh units are useful for full-screen sections and height-based layouts. Be aware that vh can behave unexpectedly on mobile due to address bar behavior.

The horizontal measurement of an element, definable as fixed pixels, percentages, or content-based sizing. Responsive designs often use percentage or max-width rather than fixed widths for flexibility. Framer's sizing controls support fixed, relative, and content-based width options.

Breakpoint Overrides are responsive design adjustments applied at specific viewport widths so elements can adapt without changing the base design.