Browser support

Site Designer exports standard HTML and CSS, so it runs in any browser that supports the CSS features you actually use in a given project.

The one thing the app handles for you

The <picture> element is not natively supported everywhere, so Site Designer ships a polyfill with the exported site. As long as JavaScript is enabled it behaves correctly even on browsers without native support; where JavaScript is off and support is missing, the default image is shown. See the Picture element.

Supporting an older browser on purpose

If you specifically need to support a browser that lacks a modern CSS feature — Grid, a blend mode, and so on — Site Designer’s real mechanism for that is Feature Queries, not a manually written @supports block. The Design For toolbar icon lets you build a fallback stylesheet for browsers that don’t support a feature, and a “Fallback First” mode for styles that should apply everywhere. See Support Queries for the full workflow.