ProtonMail (Desktop Webmail)
Supported
- align-items
- aspect-ratio
- background-blend-mode
- background-clip
- background-color
- background-image
- background-origin
- background-position
- background-repeat
- background-size
- background
- block-size & inline-size
- border-image
- border-radius
- border
- box-shadow
- box-sizing
- caption-side
- clip-path
- color-scheme CSS property
- column-count
- css column properties
- conic-gradient()
- direction
- display:flex
- display:grid
- display:none
- display
- filter
- flex-direction:column
- flex-wrap: wrap
- float
- font-stretch
- font-weight
- font shorthand
- clamp()
- max()
- min()
- gap, column-gap, row-gap
- grid-template-* properties
- height property
- inline-size
- fit-content, min-content, max-content
- justify-content
- left, right, top, bottom
- letter-spacing
- line-height
- linear-gradient()
- list-style-position
- list-style-type
- margin-inline & margin-block
- margin
- max-height property
- max-width
- min-height property
- min-width property
- mix-blend-mode
- lch(), oklch(), lab(), oklab()
- object-fit
- object-position
- opacity
- outline-offset
- outline
- overflow
- padding
- position
- :has()
- ::marker
- radial-gradient()
- rgb()
- rgba()
- scroll-snap
- system-ui, ui-serif, ui-sans-serif, ui-rounded, ui-monospace
- text-align
- text-decoration-color
- text-decoration-skip-ink
- text-decoration-thickness
- text-decoration
- text-indent
- text-overflow
- text-shadow
- text-transform
- text-underline-offset
- transform
- transition
- CSS calc() function
- ch unit
- cm unit
- em unit
- ex unit
- in unit
- initial unit
- mm unit
- pc unit
- % unit
- pt unit
- px unit
- rem unit
- vh unit
- vmax unit
- vmin unit
- vw unit
- CSS Variables (Custom Properties)
- vertical-align
- visibility
- white-space
- width property
- word-break
- writing-mode
- z-index
- <abbr> element
- address
- Local anchors
- aria-describedby attribute
- aria-hidden attribute
- aria-label attribute
- aria-labelledby attribute
- aria-live attribute
- background attribute
- <bdi> element
- <blockquote> element
- <button type="reset"> element
- <button type="submit"> element
- <code> element
- <del> element
- dir attribute
- <div> element
- HTML5 doctype
- <h1> to <h6> elements
- height attribute
- Image maps
- <img> element
- lang attribute
- <ul>, <ol> and <dl>
- loading attribute
- mailto: links
- <meter> element
- <p> element
- <pre> element
- <progress> element
- role attribute
- <rp> element
- <rt> element
- <ruby> element
- <select> element
- HTML5 semantics
- <small> element
- <span> element
- <strike> element
- <strong> element
- <style> element
- Embedded <svg> image
- <table> element
- <textarea> element
- valign attribute
- <wbr> element
- width attribute
- Animated PNG image format
- AVIF image format
- Base 64 image format
- BMP image format
- GIF image format
- ICO image format
- JPG image format
- Video as Image Assets
- PNG image format
- SVG image format
- TIFF image format
- webP image format
Partially supported
- @media
- !important keyword
- list-style
- align attribute
- <base>
- <marquee> element
- required attribute
- HEIF image format
Not supported
- AMP for Email
- BIMI
- accent-color
- animation
- @font-face
- @import
- @keyframes
- @media (-webkit-device-pixel-ratio)
- @media (orientation)
- @media (prefers-color-scheme)
- @media (prefers-reduced-motion)
- @supports
- list-style-image
- :active
- :checked
- :first-child
- :first-of-type
- :focus
- :hover
- :last-child
- :last-of-type
- :link
- :not
- :nth-child
- :nth-last-child
- :nth-last-of-type
- :nth-of-type
- :only-child
- :only-of-type
- :target
- :visited
- ::after
- ::before
- ::first-letter
- ::first-line
- ::placeholder
- Adjacent sibling combinator
- Attribute selector
- Chaining selectors
- Child combinator
- Class selector
- Descendant combinator
- General sibling combinator
- Grouping selectors
- ID selector
- Type selector
- Universal selector *
- <audio> element
- <body> element
- <dialog> element
- <form> element
- <input type="checkbox"> element
- <input type="hidden"> element
- <input type="radio"> element
- <input type="reset"> element
- <input type="submit"> element
- <input type="text"> element
- <link> element
- color-scheme meta tag
- <object> element
- <picture> element
- popover attribute
- srcset and sizes attributes
- target attribute
- <video> element
- HDR image format
Support unknown
- @media (hover), @media (any-hover)
- backdrop-filter
- border-collapse
- border-inline & border-block individual logical properties
- border-inline & border-block longhand properties
- border-inline & border-block
- border-radius logical properties
- border-spacing
- font-kerning
- font-size
- hyphens
- margin-block-start & margin-block-end
- margin-inline & margin-block
- margin-inline-start & margin-inline-end
- max-block-size
- min-inline-size
- CSS Nesting
- overflow-wrap
- padding-block-start & padding-block-end
- padding-inline & padding-block
- padding-inline-start & padding-inline-end
- lang()
- resize
- shape-margin
- shape-outside
- tab-size
- table-layout
- text-align-last
- text-decoration-line
- text-decoration-style
- text-emphasis-position
- text-emphasis
- text-orientation
- text-underline-position
- text-wrap
- user-select
- word-spacing
- <acronym> element
- <dfn> element
- hidden attribute
- <hr> element
ProtonMail (iOS)
Supported
- align-items
- aspect-ratio
- background-blend-mode
- background-clip
- background-color
- background-image
- background-origin
- background-position
- background-repeat
- background-size
- background
- block-size & inline-size
- border-image
- border-radius
- border
- box-shadow
- box-sizing
- caption-side
- clip-path
- column-count
- css column properties
- conic-gradient()
- direction
- display:flex
- display:grid
- display:none
- display
- filter
- flex-direction:column
- flex-wrap: wrap
- float
- font-stretch
- font-weight
- font shorthand
- clamp()
- max()
- min()
- gap, column-gap, row-gap
- grid-template-* properties
- height property
- inline-size
- fit-content, min-content, max-content
- justify-content
- left, right, top, bottom
- letter-spacing
- line-height
- linear-gradient()
- list-style-image
- list-style-position
- list-style-type
- list-style
- margin-inline & margin-block
- margin
- max-height property
- min-width property
- mix-blend-mode
- lch(), oklch(), lab(), oklab()
- object-fit
- object-position
- opacity
- outline-offset
- outline
- overflow
- padding
- position
- :has()
- ::marker
- radial-gradient()
- rgb()
- rgba()
- scroll-snap
- system-ui, ui-serif, ui-sans-serif, ui-rounded, ui-monospace
- text-align
- text-decoration-color
- text-decoration-skip-ink
- text-decoration-thickness
- text-indent
- text-overflow
- text-shadow
- text-transform
- text-underline-offset
- transform
- CSS calc() function
- ch unit
- cm unit
- em unit
- ex unit
- in unit
- initial unit
- mm unit
- pc unit
- % unit
- pt unit
- px unit
- rem unit
- vh unit
- vmax unit
- vmin unit
- vw unit
- CSS Variables (Custom Properties)
- vertical-align
- visibility
- white-space
- width property
- writing-mode
- z-index
- <abbr> element
- address
- align attribute
- aria-describedby attribute
- aria-hidden attribute
- aria-label attribute
- aria-labelledby attribute
- aria-live attribute
- background attribute
- <bdi> element
- <blockquote> element
- <button type="reset"> element
- <button type="submit"> element
- <code> element
- <del> element
- dir attribute
- <div> element
- <h1> to <h6> elements
- height attribute
- Image maps
- <img> element
- lang attribute
- <ul>, <ol> and <dl>
- mailto: links
- <marquee> element
- <meter> element
- <p> element
- <pre> element
- <progress> element
- role attribute
- <rp> element
- <rt> element
- <ruby> element
- <select> element
- HTML5 semantics
- <small> element
- <span> element
- <strike> element
- <strong> element
- Embedded <svg> image
- <table> element
- <textarea> element
- valign attribute
- <wbr> element
- width attribute
- Animated PNG image format
- AVIF image format
- Base 64 image format
- BMP image format
- GIF image format
- HEIF image format
- ICO image format
- JPG image format
- Video as Image Assets
- PNG image format
- SVG image format
- TIFF image format
- webP image format
Partially supported
Not supported
- AMP for Email
- BIMI
- accent-color
- animation
- @font-face
- @import
- @keyframes
- @media (-webkit-device-pixel-ratio)
- @media (orientation)
- @media (prefers-color-scheme)
- @media (prefers-reduced-motion)
- @supports
- color-scheme CSS property
- min-height property
- :active
- :checked
- :first-child
- :first-of-type
- :focus
- :hover
- :last-child
- :last-of-type
- :link
- :not
- :nth-child
- :nth-last-child
- :nth-last-of-type
- :nth-of-type
- :only-child
- :only-of-type
- :target
- :visited
- ::after
- ::before
- ::first-letter
- ::first-line
- ::placeholder
- resize
- Adjacent sibling combinator
- Attribute selector
- Chaining selectors
- Child combinator
- Class selector
- Descendant combinator
- General sibling combinator
- Grouping selectors
- ID selector
- Type selector
- Universal selector *
- text-decoration
- transition
- Local anchors
- <audio> element
- <base>
- <body> element
- <dialog> element
- HTML5 doctype
- <form> element
- <input type="checkbox"> element
- <input type="hidden"> element
- <input type="radio"> element
- <input type="reset"> element
- <input type="submit"> element
- <input type="text"> element
- <link> element
- loading attribute
- color-scheme meta tag
- <object> element
- <picture> element
- popover attribute
- required attribute
- srcset and sizes attributes
- target attribute
- <video> element
- HDR image format
Support unknown
- @media (hover), @media (any-hover)
- backdrop-filter
- border-collapse
- border-inline & border-block individual logical properties
- border-inline & border-block longhand properties
- border-inline & border-block
- border-radius logical properties
- border-spacing
- font-kerning
- font-size
- hyphens
- margin-block-start & margin-block-end
- margin-inline & margin-block
- margin-inline-start & margin-inline-end
- max-block-size
- min-inline-size
- CSS Nesting
- overflow-wrap
- padding-block-start & padding-block-end
- padding-inline & padding-block
- padding-inline-start & padding-inline-end
- lang()
- shape-margin
- shape-outside
- tab-size
- table-layout
- text-align-last
- text-decoration-line
- text-decoration-style
- text-emphasis-position
- text-emphasis
- text-orientation
- text-underline-position
- text-wrap
- user-select
- word-spacing
- <acronym> element
- <dfn> element
- hidden attribute
- <hr> element
ProtonMail (Android)
Supported
- align-items
- aspect-ratio
- @font-face
- @import
- @media (-webkit-device-pixel-ratio)
- @media
- @supports
- background-blend-mode
- background-clip
- background-color
- background-image
- background-origin
- background-position
- background-repeat
- background-size
- background
- border-image
- border-radius
- border
- box-shadow
- box-sizing
- caption-side
- clip-path
- column-count
- css column properties
- conic-gradient()
- direction
- display:flex
- display:grid
- display:none
- display
- filter
- flex-direction:column
- flex-wrap: wrap
- float
- font-weight
- font shorthand
- clamp()
- max()
- min()
- gap, column-gap, row-gap
- grid-template-* properties
- height property
- inline-size
- fit-content, min-content, max-content
- justify-content
- left, right, top, bottom
- letter-spacing
- line-height
- linear-gradient()
- list-style-position
- list-style-type
- margin-inline & margin-block
- margin
- max-height property
- max-width
- min-height property
- min-width property
- mix-blend-mode
- object-fit
- object-position
- opacity
- outline-offset
- outline
- overflow
- padding
- position
- :active
- :first-child
- :first-of-type
- :focus
- :hover
- :last-child
- :last-of-type
- :link
- :not
- :nth-child
- :nth-last-child
- :only-child
- :only-of-type
- :target
- ::after
- ::before
- ::first-letter
- ::first-line
- radial-gradient()
- rgb()
- rgba()
- scroll-snap
- Adjacent sibling combinator
- Chaining selectors
- Child combinator
- Class selector
- Descendant combinator
- General sibling combinator
- Grouping selectors
- ID selector
- Type selector
- Universal selector *
- text-align
- text-decoration-color
- text-decoration-thickness
- text-decoration
- text-indent
- text-overflow
- text-shadow
- text-transform
- text-underline-offset
- transform
- CSS calc() function
- ch unit
- cm unit
- em unit
- ex unit
- in unit
- initial unit
- mm unit
- pc unit
- % unit
- pt unit
- px unit
- rem unit
- vh unit
- vmax unit
- vmin unit
- vw unit
- CSS Variables (Custom Properties)
- vertical-align
- visibility
- white-space
- width property
- writing-mode
- z-index
- address
- align attribute
- aria-describedby attribute
- aria-hidden attribute
- aria-label attribute
- aria-labelledby attribute
- aria-live attribute
- background attribute
- <bdi> element
- <blockquote> element
- <code> element
- <del> element
- <dialog> element
- dir attribute
- <div> element
- <h1> to <h6> elements
- height attribute
- lang attribute
- <ul>, <ol> and <dl>
- <marquee> element
- <meter> element
- <p> element
- <pre> element
- <progress> element
- role attribute
- <rp> element
- <rt> element
- <ruby> element
- <select> element
- HTML5 semantics
- <small> element
- <span> element
- <strike> element
- <strong> element
- Embedded <svg> image
- <table> element
- valign attribute
- <wbr> element
- width attribute
- Animated PNG image format
- AVIF image format
- Base 64 image format
- BMP image format
- GIF image format
- ICO image format
- JPG image format
- PNG image format
- SVG image format
- webP image format
Partially supported
- !important keyword
- system-ui, ui-serif, ui-sans-serif, ui-rounded, ui-monospace
- word-break
- mailto: links
- <style> element
- <textarea> element
Not supported
- AMP for Email
- BIMI
- accent-color
- animation
- @keyframes
- @media (orientation)
- @media (prefers-color-scheme)
- @media (prefers-reduced-motion)
- color-scheme CSS property
- list-style-image
- list-style
- lch(), oklch(), lab(), oklab()
- :checked
- :has()
- :nth-last-of-type
- :nth-of-type
- :visited
- ::marker
- ::placeholder
- Attribute selector
- Local anchors
- <audio> element
- <base>
- <body> element
- <button type="reset"> element
- <button type="submit"> element
- HTML5 doctype
- <form> element
- Image maps
- <input type="checkbox"> element
- <input type="hidden"> element
- <input type="radio"> element
- <input type="reset"> element
- <input type="submit"> element
- <input type="text"> element
- <link> element
- loading attribute
- color-scheme meta tag
- <object> element
- <picture> element
- required attribute
- srcset and sizes attributes
- target attribute
- <video> element
- HDR image format
- HEIF image format
- Video as Image Assets
- TIFF image format
Support unknown
- @media (hover), @media (any-hover)
- backdrop-filter
- block-size & inline-size
- border-collapse
- border-inline & border-block individual logical properties
- border-inline & border-block longhand properties
- border-inline & border-block
- border-radius logical properties
- border-spacing
- font-kerning
- font-size
- font-stretch
- hyphens
- margin-block-start & margin-block-end
- margin-inline & margin-block
- margin-inline-start & margin-inline-end
- max-block-size
- min-inline-size
- CSS Nesting
- overflow-wrap
- padding-block-start & padding-block-end
- padding-inline & padding-block
- padding-inline-start & padding-inline-end
- lang()
- resize
- shape-margin
- shape-outside
- tab-size
- table-layout
- text-align-last
- text-decoration-line
- text-decoration-skip-ink
- text-decoration-style
- text-emphasis-position
- text-emphasis
- text-orientation
- text-underline-position
- text-wrap
- transition
- user-select
- word-spacing
- <abbr> element
- <acronym> element
- <dfn> element
- hidden attribute
- <hr> element
- <img> element
- popover attribute