Pseudo-Classes & Selectors

:focus-within

selector or pseudo-class · 6 supported, 2 partial, 5 unsupported across 21 clients

As of Sep 2, 2026, :focus-within fails or degrades in 15 of 21 email clients, treat it as progressive enhancement, never structure.

3/7 webmail, 1/6 desktop, 2/8 mobile clients support :focus-within fully.
Unsupported in Gmail, Gmail Android, Gmail iOS, Outlook 365 and 1 more.
Partial in Outlook Android, Outlook for Mac, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support :focus-within, and its replacement changes little here; see the deprecation diff.
Across all clients, only 6 of 298 tracked HTML/CSS features render identically everywhere.

Source: caniemail.com (MIT), via the Emailens engine. Last tested upstream Apr 14, 2026, synced by Emailens Sep 2, 2026.

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	Unsupported
Outlook (New)	desktop	Outlook Web	Unsupported
Outlook Classic	desktop	Microsoft Word	Unknown
Outlook iOS	mobile	Outlook Mobile	Unknown
Outlook Android	mobile	Outlook Mobile	Partial^{See caveat 1}
Outlook for Mac	desktop	WebKit	Partial^{See caveat 1}
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Unknown
Yahoo Mail	webmail	Yahoo	Supported
Yahoo Mail Android	mobile	Yahoo	Supported
Yahoo Mail iOS	mobile	Yahoo	Unknown
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Unknown
HEY Mail	webmail	WebKit	Unknown
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Supported
Fastmail	webmail	Fastmail	Unknown
Superhuman	desktop	Blink	Unknown

Documented caveats (1)

1.Outlook Android, Outlook for Mac: Partial. Only supported on type selectors.

Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.

Client-by-client behaviour for :focus-within

Fully supports :focus-within (6): Apple Mail, Yahoo Mail, Yahoo Mail Android, Samsung Mail, Proton Mail, AOL Mail.

Partial support (2): Outlook Android, Outlook for Mac. 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 365, Outlook (New). Plan fallbacks for these clients before relying on :focus-within in production sends.

Behaviour unverified in: Outlook Classic, Outlook iOS, Apple Mail iOS, Yahoo Mail iOS, Thunderbird, HEY Mail, Fastmail, Superhuman.