Modern CSS aspect-ratio Box & Video Container Generator
Generate native CSS aspect-ratio rules and legacy padding-top hack fallbacks.
Execution runs 100% locally inside the browser sandbox using HTML5 Canvas, Web Cryptography Subtle API, and Web Workers. No data is ever transmitted across the network.
Zero network latency. Operates completely offline with zero dependencies on third-party backend servers or cloud services.
Built according to official RFC specifications, cryptographic test vectors, and enterprise-grade data transformation standards.
How to Use Modern CSS aspect-ratio Box & Video Container Generator
Choose 16:9, 4:3, 1:1, 9:16, 21:9, or Custom.
Toggle @supports fallback and set image fit mode.
Copy the stylesheet directly into your project.
Frequently Asked Questions
Why is aspect-ratio important?
Aspect-ratio prevents layout shifts (CLS) by reserving exact vertical container dimensions before media assets load.
How does the fallback work?
It uses the classic padding-top percentage hack inside @supports not (aspect-ratio: ...).
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