Yahoo Mail email CSS: what breaks, and what to write instead

126 of 300 features work in Yahoo Mail · 32 partial · 142 not supported. Of the 142 not supported, 13 work in at least 14 of the other 20 clients; the other 129 work in 13 or fewer.

Works 126 · Partial 32 · Not supported 142 · Untested 0 · of 300

Yahoo · webmail · prefers-color-scheme: not supported

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@emailens/engine 0.18.22 · data last changed 10 Nov 2026

Where Yahoo Mail is the outlier

13 features work in at least 14 of the other 20 clients and are not supported here.

So an email that looks right in most clients can reach your reader in Yahoo Mail without them.

All 13

Yahoo Mail on real installs

The Emailens probe for each feature, captured on Yahoo Mail's own installs, next to the Emailens live preview of Yahoo Mail.

box-sizing in a real Yahoo Mail

The Emailens probe for box-sizing on a real Yahoo Mail — Yahoo Mail

The same probe in the Emailens live preview of Yahoo Mail — Yahoo Mail

object-fit in a real Yahoo Mail

The Emailens probe for object-fit on a real Yahoo Mail — Yahoo Mail

word-break in a real Yahoo Mail

The Emailens probe for word-break on a real Yahoo Mail — Yahoo Mail

What to write instead

13 features Yahoo Mail does not fully support have a written fix. See them in the table ↓

box-sizing

The fix for Yahoo Mail

Account for padding in width manually (no box-sizing)

after

5 lines

<div style="width: 300px;">
  <div style="padding: 20px;">
    Content; padding on inner element
  </div>
</div>

Show the original

before

4 lines

<div style="width: 300px; padding: 20px;
            box-sizing: border-box;">
  Content; total width stays 300px
</div>

Test this fix in Yahoo Mail, free

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visibility

The fix for Yahoo Mail

Use conditional comments or remove hidden content

after

5 lines

<!-- For screen readers, use font-size: 0 trick -->
<div style="font-size: 0; max-height: 0; overflow: hidden;
            mso-hide: all;" aria-hidden="true">
  Preheader text
</div>

Show the original

before

3 lines

<div style="visibility: hidden;">
  Hidden content for screen readers
</div>

Test this fix in Yahoo Mail, free

Opens the checker with this fix loaded. Uses 1 of your 3 free checks today.

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text-shadow

The fix for Yahoo Mail

Use font-weight or border-bottom as alternatives to text-shadow

after

6 lines

.glow {
  /* text-shadow is not supported in Gmail, Outlook, Yahoo.
     Use font-weight or letter-spacing for emphasis instead. */
  font-weight: bold;
  letter-spacing: 0.5px;
}

Show the original

before

3 lines

.glow {
  text-shadow: 0 0 10px rgba(255, 255, 255, 0.5);
}

Test this fix in Yahoo Mail, free

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Paste your email and see what Yahoo Mail does to it.

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No signup · Five clients free, Outlook Classic included · All 21 with an account

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Dark mode in Yahoo Mail

Not supported @media prefers-color-scheme is not supported in Yahoo Mail.

Works in 9 of 21.
Not supported color-scheme is not supported in Yahoo Mail.

Works in 4 of 21.
Not supported meta-color-scheme is not supported in Yahoo Mail.

Works in 2 of 21.

Before you send to Yahoo Mail

Inspect the wrapping container width during testing, Yahoo's injected padding can shift centered logos off-center on narrow viewports.
Verify dark-mode contrast without your prefers-color-scheme styles, since Yahoo never applies them.
Test attribute selectors in your <style> block: only [attr=value] survives, so duplicate the styling inline as a fallback.

Your next question

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Every feature in Yahoo Mail

What breaks here (174) Everything (300)

HTML Elements · 18 of 48 not supported or partial here

<abbr> Not supported Works in 14 of 21
<acronym> Not supported Works in 13 of 21
<address> Works Works in 20 of 21
<audio> Not supported Works in 4 of 21
<base> Buggy. Partial Works in 4 of 21
<bdi> Not supported Works in 6 of 21
<blockquote> Works Works in 19 of 21
<body> Partial. Partial Works in 5 of 21
<button type="reset"> Not supported Works in 10 of 21
<button type="submit"> Works Works in 11 of 21
<code> Works Works in 20 of 21
<del> Works Works in 20 of 21
<dfn> Works Works in 17 of 21
<dialog> Not supported Works in 5 of 21
<div> Works Works in 20 of 21
<form> fix Observed 2026-10-29 (Emailens probe, Yahoo Mail web (Chrome), our own seed inbox): The form is kept but its action is removed (absolute, relative and empty alike), and so is formaction on a button; Yahoo adds target="_blank". Not supported Works in 10 of 21
<h1> Works Works in 20 of 21
<hr> Works Works in 18 of 21
<img> Works Works in 19 of 21
<input type="checkbox"> Works Works in 16 of 21
<input type="hidden"> Works Works in 16 of 21
<input type="radio"> Works Works in 16 of 21
<input type="reset"> Works Works in 15 of 21
<input type="submit"> Works Works in 12 of 21
<input type="text"> Works Works in 13 of 21
<link> fix Not supported Works in 3 of 21
<marquee> The <marquee> element is supported but the animation doesn't play in Internet Explorer or Firefox. Partial Works in 8 of 21
<meter> Not supported Works in 11 of 21
<object> Not supported Works in 1 of 21
<p> Works Works in 20 of 21
<picture> Not supported Works in 4 of 21
<pre> Works Works in 20 of 21
<progress> Not supported Works in 6 of 21
<rp> Works Works in 15 of 21
<rt> Works Works in 15 of 21
<ruby> Works Works in 15 of 21
<select> Works Works in 14 of 21
<small> Works Works in 20 of 21
<span> Works Works in 20 of 21
<strike> Works Works in 17 of 21
<strong> Works Works in 20 of 21
<style> Works Works in 16 of 21
<svg> fix Not supported Works in 5 of 21
<table> Works Works in 20 of 21
<textarea> Works Works in 13 of 21
<ul> Partial. Partial Works in 7 of 21
<video> fix <video>, <source> and <track> tags are stripped. Not supported Works in 3 of 21
<wbr> Works Works in 16 of 21

HTML Attributes · 14 of 22 not supported or partial here

[align] Works Works in 17 of 21
[aria-describedby] Not supported Works in 9 of 21
[aria-hidden] Not supported Works in 13 of 21
[aria-label] Not supported Works in 13 of 21
[aria-labelledby] Not supported Works in 7 of 21
[aria-live] Not supported Works in 8 of 21
[background] Works Works in 16 of 21
[cellpadding] Works Works in 18 of 21
[cellspacing] Works Works in 18 of 21
[command] Not supported Works in 3 of 21
[dir] Works Works in 19 of 21
[height] Works Works in 18 of 21
[hidden] Not supported Works in 5 of 21
[lang] Not supported on <td> elements. Partial Works in 15 of 21
[loading] Not supported Works in 4 of 21
[popover] Not supported Works in 3 of 21
[required] Not supported Works in 7 of 21
[role] Partial. Partial Works in 14 of 21
[srcset] Not supported Works in 4 of 21
[target] Not supported. Not supported Works in 0 of 21
[valign] Works Works in 20 of 21
[width] Works Works in 18 of 21

HTML & Email Structure · 3 of 8 not supported or partial here

amp4email Works Works in 6 of 21
anchor-links Partial. Partial Works in 12 of 21
doctype Works Works in 13 of 21
html-comments Works Works in 18 of 21
html5-semantics Unsupported opening and closing tags are stripped. Not supported Works in 6 of 21
image-maps Works Works in 15 of 21
mailto-links Works Works in 17 of 21
meta-color-scheme Not supported Works in 2 of 21

CSS At-Rules · 8 of 10 not supported or partial here

@font-face Not supported Works in 6 of 21
@import Not supported Works in 4 of 21
@keyframes Works Works in 7 of 21
@media Partial. Partial Works in 5 of 21
@media device-pixel-ratio Not supported Works in 10 of 21
@media hover Not supported Works in 9 of 21
@media orientation Not supported Works in 11 of 21
@media prefers-color-scheme Not supported. Not supported Works in 9 of 21
@media prefers-reduced-motion Not supported Works in 9 of 21
@supports Works Works in 9 of 21

Pseudo-Elements · 2 of 6 not supported or partial here

::after Not supported Works in 6 of 21
::before Not supported Works in 6 of 21
::first-letter Works Works in 10 of 21
::first-line Works Works in 10 of 21
::marker Works Works in 10 of 21
::placeholder Works Works in 9 of 21

Pseudo-Classes & Selectors · 8 of 34 not supported or partial here

:adjacent-sibling Works Works in 16 of 21
:attribute-selector Partial. Partial Works in 6 of 21
:chaining Works Works in 14 of 21
:checked Works Works in 9 of 21
:child-combinator Works Works in 16 of 21
:class-selector Works Works in 17 of 21
:descendant-combinator Works Works in 17 of 21
:first-child Works Works in 12 of 21
:first-of-type Works Works in 12 of 21
:focus Works Works in 10 of 21
:focus-visible Works Works in 6 of 21
:focus-within Works Works in 6 of 21
:general-sibling Works Works in 16 of 21
:grouping Works Works in 17 of 21
:has Not supported. Not supported Works in 5 of 21
:hover Works Works in 12 of 21
:id-selector Works Works in 17 of 21
:lang Not supported Works in 6 of 21
:last-child Works Works in 12 of 21
:last-of-type Works Works in 12 of 21
:link Works Works in 13 of 21
:not Not supported Works in 6 of 21
:nth-child Not supported. Not supported Works in 6 of 21
:nth-last-child Not supported. Not supported Works in 6 of 21
:nth-of-type Not supported. Not supported Works in 6 of 21
:only-child Works Works in 12 of 21
:only-of-type Works Works in 12 of 21
:target Works Works in 7 of 21
:type-selector Works Works in 17 of 21
:universal-selector Works Works in 16 of 21
:visited Works Works in 8 of 21
pseudo-class-active Works Works in 8 of 21
pseudo-class-default Works Works in 10 of 21
pseudo-class-nth-last-of-type Not supported. Not supported Works in 6 of 21

CSS Functions · 8 of 8 not supported or partial here

calc Not supported Works in 8 of 21
clamp Not supported Works in 6 of 21
conic-gradient Not supported Works in 6 of 21
fit-content Not supported Works in 11 of 21
linear-gradient Not supported Works in 9 of 21
max Not supported Works in 6 of 21
min Not supported Works in 6 of 21
radial-gradient Not supported Works in 10 of 21

CSS Properties · 113 of 164 not supported or partial here

!important Partial. Partial Works in 11 of 21
accent-color Not supported Works in 5 of 21
align-items Not supported Works in 13 of 21
animation fix Not supported Works in 5 of 21
aspect-ratio Not supported Works in 5 of 21
backdrop-filter Not supported Works in 6 of 21
background Partial. Partial Works in 16 of 21
background-blend-mode Not supported Works in 13 of 21
background-clip Not supported Works in 14 of 21
background-color Works Works in 21 of 21
background-image Partial. Partial Works in 16 of 21
background-origin Not supported Works in 14 of 21
background-position Works Works in 20 of 21
background-repeat Works Works in 20 of 21
background-size Observed 2026-11-09 (Emailens real-device checks, Yahoo Mail web (Chrome): foodpanda campaign (2026-10-28), AliExpress (2026-11-09)): Partial. Partial Works in 17 of 21
bimi Works Works in 9 of 21
block-size Not supported Works in 7 of 21
border Works Works in 20 of 21
border-collapse Works Works in 19 of 21
border-image Not supported Works in 7 of 21
border-inline Not supported Works in 3 of 21
border-inline-individual Not supported Works in 3 of 21
border-inline-longhand Not supported Works in 4 of 21
border-radius Partial support. Partial Works in 16 of 21
border-radius-logical Not supported Works in 3 of 21
border-spacing Works Works in 17 of 21
bottom Not supported Works in 11 of 21
box-shadow Works Works in 14 of 21
box-sizing fix Not supported Works in 16 of 21
caption-side Works Works in 20 of 21
clear Partial. Partial Works in 9 of 21
clip-path Not supported Works in 8 of 21
color Works Works in 21 of 21
color-scheme Not supported Works in 4 of 21
column-count Not supported Works in 16 of 21
columns Not supported Works in 16 of 21
css-comments Works Works in 14 of 21
cursor Partial. Partial Works in 2 of 21
custom-properties Not supported Works in 6 of 21
direction Works Works in 21 of 21
display Partial. Partial Works in 13 of 21
display:flex Works Works in 18 of 21
display:grid Works Works in 18 of 21
display:none Works Works in 20 of 21
empty-cells Works Works in 14 of 21
filter Not supported Works in 7 of 21
flex Observed 2026-10-27 (Emailens probe, Yahoo Mail web (Chrome), real-device run E8fVpFwwLtL8): The flex shorthand is dropped: an item at flex:0 0 34% shrank to its narrowest, breaking words letter by letter. Not supported Works in 13 of 21
flex-basis Observed 2026-10-27 (Emailens probe, Yahoo Mail web (Chrome), real-device run E8fVpFwwLtL8): Dropped, with flex-grow and flex-shrink beside it: the item sized to its content instead of 34%. Not supported Works in 13 of 21
flex-direction Not supported Works in 12 of 21
flex-wrap Not supported Works in 13 of 21
float Partial. Partial Works in 14 of 21
font Works Works in 20 of 21
font-family Works Works in 21 of 21
font-kerning Not supported Works in 13 of 21
font-size Partial support. Partial Works in 13 of 21
font-size-adjust 2-value syntax is supported, but the first value (font-metric) is ignored. Partial Works in 10 of 21
font-stretch Not supported Works in 10 of 21
font-weight Partial support. Partial Works in 16 of 21
gap fix Not supported Works in 7 of 21
grid-template-columns Not supported Works in 7 of 21
height Buggy. Not supported Works in 16 of 21
hyphenate-character Not supported Works in 4 of 21
hyphenate-limit-chars Not supported Works in 1 of 21
hyphens Not supported Works in 4 of 21
inert Not supported Works in 3 of 21
inline-size Not supported Works in 4 of 21
inset Not supported Works in 3 of 21
justify-content Not supported Works in 13 of 21
left Not supported Works in 11 of 21
letter-spacing Works Works in 20 of 21
light-dark Not supported Works in 3 of 21
line-height Works Works in 20 of 21
list-style list-style-image values are not supported but the rest of the list-style property is kept. Partial Works in 11 of 21
list-style-image Not supported Works in 6 of 21
list-style-position Works Works in 19 of 21
list-style-type Works Works in 21 of 21
margin Partial. Partial Works in 8 of 21
margin-block-start-end Not supported Works in 4 of 21
margin-inline-block Not supported Works in 6 of 21
margin-inline-start-end Not supported Works in 4 of 21
mask-image Not supported Works in 4 of 21
max-block-size Not supported Works in 5 of 21
max-height Works Works in 20 of 21
max-inline-size Not supported Works in 4 of 21
max-width Works Works in 20 of 21
min-block-size Not supported Works in 4 of 21
min-height Works Works in 19 of 21
min-inline-size Not supported Works in 5 of 21
min-width Works Works in 20 of 21
mix-blend-mode Not supported Works in 13 of 21
modern-color Not supported Works in 4 of 21
nesting Not supported. Not supported Works in 2 of 21
object-fit Not supported Works in 14 of 21
object-position Not supported Works in 14 of 21
opacity Works Works in 19 of 21
orphans Not supported Works in 10 of 21
outline Works Works in 20 of 21
outline-offset Not supported Works in 7 of 21
overflow Partial. Partial Works in 4 of 21
overflow-wrap fix Not supported Works in 2 of 21
padding Works Works in 20 of 21
padding-block-start-end Not supported Works in 4 of 21
padding-inline-block Not supported Works in 3 of 21
padding-inline-start-end Not supported Works in 4 of 21
position fix Partial. Partial Works in 2 of 21
resize resize property is stripped from style tag Not supported Works in 1 of 21
rgb Whitespace syntax is not supported (rgb(0 128 0 / 1)). Partial Works in 12 of 21
rgba Whitespace syntax is not supported (rgb(0 128 0 / 1)). Partial Works in 12 of 21
right Not supported Works in 11 of 21
scroll-snap Not supported Works in 6 of 21
shape-margin Not supported Works in 6 of 21
shape-outside Not supported Works in 6 of 21
system-ui Works Works in 12 of 21
tab-size Not supported Works in 8 of 21
table-layout Works Works in 16 of 21
text-align Partial. Partial Works in 13 of 21
text-align-last Not supported Works in 7 of 21
text-decoration Works Works in 14 of 21
text-decoration-color Works Works in 17 of 21
text-decoration-line Works Works in 16 of 21
text-decoration-skip-ink Not supported Works in 7 of 21
text-decoration-style Works Works in 16 of 21
text-decoration-thickness Not supported Works in 7 of 21
text-emphasis Not supported Works in 9 of 21
text-emphasis-position Not supported Works in 4 of 21
text-indent Partial. Partial Works in 13 of 21
text-justify Partial. Partial Works in 0 of 21
text-orientation Not supported Works in 13 of 21
text-overflow Not supported Works in 13 of 21
text-shadow fix Observed 2026-11-08 (Emailens probe sheets 20-22, Yahoo Mail web (Chrome), our own seed inbox): A green text-shadow did not draw; the text rendered plain. Not supported Works in 12 of 21
text-transform Works Works in 20 of 21
text-underline-offset Not supported Works in 7 of 21
text-underline-position Not supported Works in 8 of 21
text-wrap Not supported Works in 4 of 21
top Not supported Works in 11 of 21
transform fix Not supported Works in 7 of 21
transition Partial. Partial Works in 4 of 21
unit-ch Not supported Works in 15 of 21
unit-cm Works Works in 20 of 21
unit-em Works Works in 20 of 21
unit-ex Works Works in 20 of 21
unit-in Works Works in 20 of 21
unit-initial Not supported Works in 12 of 21
unit-mm Works Works in 20 of 21
unit-pc Works Works in 20 of 21
unit-percent Works Works in 20 of 21
unit-pt Works Works in 20 of 21
unit-px Works Works in 20 of 21
unit-rem Not supported Works in 15 of 21
unit-vh Works Works in 17 of 21
unit-vmax Not supported Works in 15 of 21
unit-vmin Not supported Works in 15 of 21
unit-vw Works Works in 18 of 21
user-select Property is stripped from style tag Not supported Works in 3 of 21
vertical-align Works Works in 21 of 21
visibility fix Observed 2026-11-08 (Emailens probe sheets 20-22, Yahoo Mail web (Chrome), our own seed inbox): An element at visibility:hidden stayed visible. Not supported Works in 13 of 21
white-space Works Works in 15 of 21
white-space-collapse Not supported Works in 4 of 21
widows Not supported Works in 10 of 21
width Works Works in 20 of 21
word-break fix Not supported Works in 4 of 21
word-spacing Does not support rem and ch values. Partial Works in 14 of 21
writing-mode Not supported Works in 13 of 21
z-index Works Works in 17 of 21

How Yahoo Mail renders email

Yahoo Mail supports <style> blocks, flexbox and media queries limited to screen, min-width, max-width, min-height and max-height. It rewrites some of your CSS on the way in and adds its own wrapper styles, which can affect layout, and it does not support web fonts or dark-mode media queries.

Wrapper styles: Yahoo wraps your email in its own container with additional styles. This can affect max-width calculations and centering. Always test your email's outer wrapper behavior.
CSS attribute selectors: Only the [attr=value] form is supported. Other attribute selectors are dropped, so prefer class selectors in your <style> block.
background shorthand: Partially supported: multiple backgrounds lose the comma between values, and the / background-size form is not supported. Use the individual properties instead.

Yahoo Mail injects a wrapping container that applies its own padding and max-width. Designs that depend on full edge-to-edge rendering should account for an extra ~16-24px of horizontal padding inserted by the client.
The Yahoo sanitizer rewrites the background shorthand into individual properties. Explicitly declaring background-color, background-image, background-repeat, and background-position avoids dropped values during the rewrite.
Media queries work when they use screen, min-width, max-width, min-height or max-height. Anything else, including orientation and prefers-color-scheme, is not supported.
@font-face is not supported, so web fonts never load. Always supply a complete system font stack.