Pseudo-Classes & Selectors

pseudo-class-default

CSS property · 6 supported, 1 partial, 5 unsupported across 15 clients

Client Support

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

Client-by-client behaviour for pseudo-class-default

Fully supports pseudo-class-default (6): Outlook iOS, Outlook Android, Apple Mail, Apple Mail iOS, Yahoo Mail, Thunderbird.

Partial support (1): Outlook 365. Expect rendering quirks unique to each engine — partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (5): Gmail, Gmail Android, Gmail iOS, Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on pseudo-class-default in production sends.

Behaviour unverified in: Samsung Mail, HEY Mail, Superhuman.