Thunderbird
Thunderbird is Mozilla's open-source desktop email client. Review CSS and HTML support across versions.
About Thunderbird
Thunderbird is Mozilla's open-source email client. It uses the Gecko rendering engine and has reasonably good CSS support, similar to Firefox. It's popular among power users and enterprises.
CSS & Design Tips
- Thunderbird supports most CSS properties that Firefox supports
- Media queries and responsive design work well
- Avoid browser-specific prefixes; Thunderbird interprets some incorrectly
- Performance is generally better with simpler CSS
- The mobile version (K-9 Mail) has different CSS support characteristics
Best Practices
Thunderbird users are often technically savvy and have modern clients. Use standards-compliant CSS and avoid vendor prefixes. Test responsiveness and focus on accessibility.
Supported Features
align-items
css
animation
css
@font-face
css
@import
css
@keyframes
css
@media (orientation)
css
@media (prefers-color-scheme)
css
@media
css
@supports
css
background-blend-mode
css
background-clip
css
background-color
css
background-image
css
background-origin
css
background-position
css
background-repeat
css
background-size
css
background
css
block-size & inline-size
css
border-collapse
css
border-image
css
border-radius
css
border-spacing
css
border
css
box-shadow
css
box-sizing
css
caption-side
css
clip-path
css
color-scheme CSS property
css
column-count
css
css column properties
css
CSS comments
css
conic-gradient()
css
cursor
css
direction
css
display:flex
css
display:grid
css
display:none
css
display
css
filter
css
flex-direction:column
css
flex-wrap: wrap
css
float
css
font-kerning
css
font-size
css
font-stretch
css
font-weight
css
font shorthand
css
clamp()
css
light-dark()
css
max()
css
min()
css
gap, column-gap, row-gap
css
grid-template-* properties
css
height property
css
!important keyword
css
inline-size
css
inset
css
fit-content, min-content, max-content
css
justify-content
css
left, right, top, bottom
css
letter-spacing
css
line-height
css
linear-gradient()
css
list-style-image
css
list-style-position
css
list-style-type
css
list-style
css
margin-inline & margin-block
css
margin
css
max-height property
css
max-width
css
min-height property
css
min-width property
css
mix-blend-mode
css
CSS Nesting
css
object-fit
css
object-position
css
opacity
css
outline-offset
css
outline
css
overflow
css
padding
css
position
css
:active
css
:checked
css
:first-child
css
:first-of-type
css
:focus
css
:hover
css
:last-child
css
:last-of-type
css
:link
css
:not
css
:nth-child
css
:nth-last-child
css
:nth-last-of-type
css
:nth-of-type
css
:only-child
css
:only-of-type
css
:target
css
:visited
css
::after
css
::before
css
::first-letter
css
::first-line
css
::marker
css
::placeholder
css
radial-gradient()
css
rgb()
css
rgba()
css
scroll-snap
css
Adjacent sibling combinator
css
Attribute selector
css
Chaining selectors
css
Child combinator
css
Class selector
css
Descendant combinator
css
General sibling combinator
css
Grouping selectors
css
ID selector
css
Type selector
css
Universal selector *
css
shape-margin
css
shape-outside
css
text-align
css
text-decoration-color
css
text-decoration-line
css
text-decoration-skip-ink
css
text-decoration-style
css
text-decoration-thickness
css
text-decoration
css
text-indent
css
text-orientation
css
text-overflow
css
text-shadow
css
text-transform
css
text-underline-offset
css
text-underline-position
css
transform
css
transition
css
CSS calc() function
css
ch unit
css
cm unit
css
em unit
css
ex unit
css
in unit
css
initial unit
css
mm unit
css
pc unit
css
% unit
css
pt unit
css
px unit
css
rem unit
css
vh unit
css
vmax unit
css
vmin unit
css
vw unit
css
CSS Variables (Custom Properties)
css
vertical-align
css
visibility
css
white-space
css
width property
css
word-break
css
word-spacing
css
writing-mode
css
z-index
css
Not Supported
43 CSS features are not supported by Thunderbird.
Show 43 unsupported features
accent-color
css
aspect-ratio
css
@media (-webkit-device-pixel-ratio)
css
@media (hover), @media (any-hover)
css
@media (prefers-reduced-motion)
css
backdrop-filter
css
border-inline & border-block individual logical properties
css
border-inline & border-block longhand properties
css
border-inline & border-block
css
border-radius logical properties
css
clear
css
empty-cells
css
hyphenate-character
css
hyphenate-limit-chars
css
hyphens
css
margin-block-start & margin-block-end
css
margin-inline-start & margin-inline-end
css
mask-image
css
max-block-size
css
max-inline-size
css
min-block-size
css
min-inline-size
css
lch(), oklch(), lab(), oklab()
css
orphans
css
overflow-wrap
css
padding-block-start & padding-block-end
css
padding-inline & padding-block
css
padding-inline-start & padding-inline-end
css
:has()
css
lang()
css
resize
css
system-ui, ui-serif, ui-sans-serif, ui-rounded, ui-monospace
css
tab-size
css
table-layout
css
text-align-last
css
text-emphasis-position
css
text-emphasis
css
text-justify
css
text-wrap
css
user-select
css
white-space-collapse
css
widows
css
word-wrap
css