CSS Properties

system-ui

CSS property · 8 supported, 4 partial, 2 unsupported across 15 clients

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Partial
Gmail iOS	mobile	Gmail Mobile	Supported
Outlook 365	webmail	Outlook Web	Supported
Outlook (New)	desktop	Outlook Web	Unsupported
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Supported
Outlook Android	mobile	Outlook Mobile	Partial
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Supported
Samsung Mail	mobile	Samsung	Partial
Thunderbird	desktop	Gecko	Partial
HEY Mail	webmail	WebKit	Supported
Superhuman	desktop	Blink	Unknown

Client-by-client behaviour for system-ui

Fully supports system-ui (8): Gmail, Gmail iOS, Outlook 365, Outlook iOS, Apple Mail, Apple Mail iOS, Yahoo Mail, HEY Mail.

Partial support (4): Gmail Android, Outlook Android, Samsung Mail, Thunderbird. Expect rendering quirks unique to each engine — partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (2): Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on system-ui in production sends.

Behaviour unverified in: Superhuman.