Fastmail
Engine: Fastmail·webmail·Dark mode: Yes
CSS coverage profile for Fastmail
Fastmail renders with the Fastmail engine and supports 163 of 255 tracked CSS and HTML features fully, with 4 partially supported and 29 unsupported. That places it in a moderate coverage band.
A meaningful portion of CSS is unsupported or partially supported. Plan fallbacks for layout-critical features and validate every template before send.
163
Supported
4
Partial
29
Unsupported
255
Total
HTML Elements40
| Feature | Support |
|---|---|
| <abbr> | Supported |
| <acronym> | Unknown |
| <address> | Supported |
| <audio> | Unsupported |
| <base> | Partial |
| <bdi> | Supported |
| <blockquote> | Supported |
| <body> | Unsupported |
| <code> | Supported |
| <del> | Supported |
| <dfn> | Unknown |
| <dialog> | Unsupported |
| <div> | Supported |
| <form> | Unsupported |
| <h1> | Supported |
| <hr> | Unknown |
| <img> | Supported |
| <link> | Unsupported |
| <marquee> | Unsupported |
| <meter> | Supported |
| <object> | Unsupported |
| <p> | Supported |
| <picture> | Unsupported |
| <pre> | Supported |
| <progress> | Supported |
| <rp> | Supported |
| <rt> | Supported |
| <ruby> | Supported |
| <select> | Supported |
| <small> | Supported |
| <span> | Supported |
| <strike> | Supported |
| <strong> | Supported |
| <style> | Supported |
| <svg> | Unsupported |
| <table> | Supported |
| <textarea> | Supported |
| <ul> | Supported |
| <video> | Unsupported |
| <wbr> | Supported |
CSS At-Rules5
| Feature | Support |
|---|---|
| @font-face | Unsupported |
| @import | Unsupported |
| @keyframes | Supported |
| @media | Supported |
| @supports | Unsupported |
Pseudo-Elements6
| Feature | Support |
|---|---|
| ::after | Supported |
| ::before | Supported |
| ::first-letter | Supported |
| ::first-line | Supported |
| ::marker | Supported |
| ::placeholder | Supported |
Pseudo-Classes & Selectors34
| Feature | Support |
|---|---|
| :adjacent-sibling | Supported |
| :attribute-selector | Supported |
| :chaining | Supported |
| :checked | Supported |
| :child-combinator | Supported |
| :class-selector | Supported |
| :descendant-combinator | Supported |
| :first-child | Supported |
| :first-of-type | Supported |
| :focus | Supported |
| :focus-visible | Unknown |
| :focus-within | Unknown |
| :general-sibling | Supported |
| :grouping | Supported |
| :has | Supported |
| :hover | Supported |
| :id-selector | Supported |
| :lang | Unknown |
| :last-child | Supported |
| :last-of-type | Supported |
| :link | Supported |
| :not | Supported |
| :nth-child | Supported |
| :nth-last-child | Supported |
| :nth-of-type | Supported |
| :only-child | Supported |
| :only-of-type | Supported |
| :target | Unsupported |
| :type-selector | Supported |
| :universal-selector | Supported |
| :visited | Supported |
| pseudo-class-active | Supported |
| pseudo-class-default | Unknown |
| pseudo-class-nth-last-of-type | Supported |
CSS Functions8
| Feature | Support |
|---|---|
| calc | Supported |
| clamp | Unsupported |
| conic-gradient | Supported |
| fit-content | Supported |
| linear-gradient | Supported |
| max | Unsupported |
| min | Unsupported |
| radial-gradient | Supported |
CSS Properties162
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Try Emailens FreeSupport data last updated Apr 27, 2026 · synced from caniemail.com via @emailens/engine.