CSS Functions

fit-content

CSS function · 10 supported, 3 partial, 7 unsupported across 21 clients

fit-content() returns a size that grows to its content but caps at a given maximum. It is used as both a sizing keyword and a function in modern CSS, and email support is limited , Apple Mail honors it, while Outlook and Gmail ignore it. For email, traditional table cell widths remain the most reliable sizing mechanism.

Client Support

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

Client-by-client behaviour for fit-content

Fully supports fit-content (10): Gmail, Gmail Android, Outlook 365, Outlook for Mac, Apple Mail, Apple Mail iOS, Thunderbird, HEY Mail, Proton Mail, Fastmail.

Partial support (3): Gmail iOS, Outlook iOS, Outlook Android. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (7): Outlook (New), Outlook Classic, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, AOL Mail. Plan fallbacks for these clients before relying on fit-content in production sends.

Behaviour unverified in: Superhuman.

When to use fit-content in email

Sizing a button to its label without a fixed width.
Fluid card sizing in modern-client-only layouts.
Constraining a content block to its natural width while capping at a max.

Rendering behaviour and edge cases

Outlook on Windows ignores fit-content() entirely.
Apple Mail supports it in recent versions.
Behavior on Gmail Web varies between Chromium versions.

Recommended fallback strategy

Use fit-content() only as progressive enhancement. Provide a fixed pixel width or a width attribute on table cells as the baseline so non-supporting clients still receive a sensible size.