The `border-radius` on the `| ` will be ignored in Outlook — the button will appear square. This is an acceptable degradation. The button remains functional in every client.
***
## Dark Mode
Many email clients now support dark mode, which can dramatically change how your email looks. Clients handle dark mode differently:
| Behavior | Clients |
| --------------------------------------------------------------- | --------------------------- |
| **No change** — respects your colors as-is | Some Outlook configurations |
| **Partial inversion** — darkens light backgrounds, adjusts text | Gmail, Outlook (web) |
| **Full inversion** — inverts all colors | Some Android clients |
| **Respects `prefers-color-scheme`** — uses your dark mode CSS | Apple Mail, Thunderbird |
### Defensive Dark Mode Strategies
* Use **transparent backgrounds** where possible instead of white — they adapt naturally to dark mode.
* Avoid pure white (`#ffffff`) backgrounds — use a very light gray (`#f8f8f8`) that dark mode engines transform more gracefully.
* **Add a thin transparent border** around logos on transparent backgrounds to prevent them from disappearing against dark backgrounds.
* For Apple Mail, provide explicit dark mode styles via the `prefers-color-scheme` media query (this only works where ` | 
```
### Buttons
CSS-styled buttons (`border-radius`, `background-color` on `` tags) do not render in Outlook. Use a hybrid approach with VML fallback, or use a table-based button:
```html theme={null}