Selector or pseudo-class · data last changed 10 Nov 2026
:universal-selector in email clients
Works in 16 of 21. Not supported in Outlook Classic and Proton Mail. Partial in Gmail Android and Gmail iOS. Untested in Superhuman.
Your reader in Outlook Classic sees the email without :universal-selector, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
Avoid relying on * for production emails. If you need a global reset, apply explicit inline styles on each element instead. Reserve the universal selector for niche progressive-enhancement cases in modern clients only.
There is no drop-in fix for :universal-selector in Outlook Classic. Design so the email still reads without it.
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:universal-selector is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Outlook Classic | Not supported |
| Proton Mail | Not supported |
| Gmail Android | Partial See caveat 1 |
| Gmail iOS | Partial See caveat 1 |
| Superhuman | Untested |
Works in 16: Gmail, Outlook 365, Outlook (New) and 13 more. Show all
| Client | Support |
|---|---|
| Gmail | Works |
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Yahoo Mail | Works |
| Yahoo Mail Android | Works |
| Yahoo Mail iOS | Works |
| Samsung Mail | Works |
| Thunderbird | Works |
| HEY Mail | Works |
| AOL Mail | Works |
| Fastmail | Works |
Caveats (1)
- 1. Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts.
Caveats as recorded by caniemail (MIT), one entry per wording.
How :universal-selector behaves
The universal selector (*) matches every element. It is occasionally used in email for a single global rule like setting box-sizing: border-box, but its specificity is extremely low and Outlook Classic does not support it. In practice, the universal selector is a niche progressive enhancement.
- Specificity is the lowest possible, any other selector overrides *.
- Outlook Classic ignores * because <style> is stripped.
- Universal selectors can have measurable rendering cost on slow clients with large emails.
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