Does CSS CSS Variables (Custom Properties) Work in HTML Email?
Custom properties that hold reusable values, referenced elsewhere with var(), enabling theme-like CSS patterns.
Does CSS Variables (Custom Properties) work in HTML email?
The CSS CSS Variables (Custom Properties) property is supported in Outlook (Mac / Web), Apple Mail, Samsung Email, Thunderbird, and others. It is NOT supported in Gmail, Outlook (Windows), Yahoo! Mail, and others. Always include a safe fallback for unsupported clients.
Which Email Clients Support CSS CSS Variables (Custom Properties)?
CSS support for CSS Variables (Custom Properties) across email clients
| Email Client | Desktop | Mobile / Web | Notes |
|---|---|---|---|
| Gmail | ✗ No | ✗ No | — |
| Outlook (Windows) | ✗ No | ? | — |
| Outlook (Mac / Web) | ✓ Yes | ✗ No | — |
| Apple Mail | ✓ Yes | ✓ Yes | — |
| Yahoo! Mail | ✗ No | ✗ No | — |
| Samsung Email | ? | ✓ Yes | — |
| Thunderbird | ✓ Yes | ? | — |
| ProtonMail | ✓ Yes | ✓ Yes | — |
| Fastmail | ✗ No | ? | — |
Notes
- #1 Partial. The `var()` function is supported, but not the variable declaration.
- #2 Partial. Not supported with non Google accounts.
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