A Guide To CSS Support In Browsers

A Guide To CSS Support In Browsers A Guide To CSS Support In
Browsers Rachel Andrew 2019-02-04T12:00:00+01:00

We will never live in a world where everyone viewing our sites
has an identical browser and browser version, just as we will never
live in a world where everyone has the same size screen and
resolution. This means that dealing with old browsers — or
browsers which do not support something that we want to use — is
part of the job of a web developer. That said, things are far
better now than in the past, and in this article, I’m going to
have a look at the different types of browser support issues we
might run into. I’m going to show you some ways to deal with
them, and also look at things which might be coming soon which can

Why Do We Have These Differences?

Even in a world where the majority of browsers are
Chromium-based, those browsers are not all running the same version
of Chromium as Google Chrome. This means that a Chromium-based
browser such as Vivaldi, might be a few versions behind Google

And, of course, users do not always quickly update their
browsers, although that situation has improved in recent years with
most browsers silently upgrading themselves.

There is also the manner in which new features get into browsers
in the first place. It is not the case that new features for CSS
are designed by the CSS Working Group, and a complete spec handed
down to browser vendors with an instruction to implement it. Quite
often it is only when an experimental implementation happens, that
all the finer details of the specification can be worked out.
Therefore, feature development is an iterative
and requires that browsers implement these
specifications in development. While implementation happens these
days most often behind a flag in the browser or available only in a
Nightly or preview version, once a browser has a complete feature,
it is likely to switch it on for everyone even if no other browser
yet has support.

All this means that — as much as we might like it — we will
never exist in a world where features are magically available on
every desktop and phone simultaneously. If you are a professional
web developer then your job is to deal with that fact.

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Bugs vs. Lack Of Support

There are three issues that we face with regard to browser

  1. No
    Support Of A Feature

    The first issue (and easiest to deal with) is when a browser does
    not support the feature at all.

  2. Dealing With Browser “Bugs”

    The second is when the browser claims to support the feature, but
    does so in a way that is different to the way that other browsers
    support the feature. Such an issue is what we tend to refer to as a
    “browser bug” because the end result is inconsistent

  3. Partial Support Of CSS Properties

    This one is becoming more common; a situation in which a browser
    supports a feature — but only in one context.

It’s helpful to understand what you are dealing with when you
see a difference between browsers, so let’s have a look at each
of these issues in turn.

1. No Support Of A Feature

If you use a CSS property or value that a browser does not
understand, the browser will ignore it. This is the same whether
you use a feature that is unsupported, or make up a feature and try
to use it. If the browser does not understand that line of CSS, it
just skips it and gets on with the next thing it does

This design principle of CSS means that you can cheerfully use
new features, in the knowledge that nothing bad will happen to a
browser that doesn’t have support. For some CSS, used purely as
an enhancement, that is all you need to do. Use the feature, make
sure that when that feature is not available the experience is
still good, and that’s it. This approach is the basic idea behind
progressive enhancement, using this feature of the platform which
enables the safe use of new things in browsers which don’t
understand them.

If you want to check whether a feature you are using is
supported by browsers then you can look at the Can I Use website. Another good place to
look for fine-grained support information is the page for each CSS
property on MDN.
The browser support data there tends to be very detailed.

New CSS Understands Old CSS

As new CSS features are developed, care is taken in terms of how
they interact with existing CSS. For example, in the Grid and
Flexbox specification, it is detailed in terms of how display: grid
and display: flex deal with scenarios such as when a floated item
becomes a grid item, or a multicol container is turned into a grid.
This means that certain behaviors are ignored, helping you to
simply overwrite the CSS for the nonsupporting browser. These
overrides are detailed in the page for
Progressive enhancement and Grid Layout on MDN

Detecting Support With Feature Queries

The above method only works if the CSS you need to use does not
need other properties to go along with it. You might need to add
additional properties to your CSS for older browsers which would
then also be interpreted by the browsers which support the feature

A good example of this can be found when using Grid Layout.
While a floated item which becomes a grid item loses all float
behavior, it is likely that if you are trying to create a fallback
for a grid layout with float, you will have added percentage widths
and possibly margins to the items.

.grid > .item {
    width: 23%;
    margin: 0 1%;

A four column layout Using floats we can
create a four column layout, widths and margins need to be set in
%. (Large

These widths and margins will then still apply when the floated
item is a grid item. The width becomes a percentage of the grid
track rather than the full width of the container; any margin will
then be applied as well as a gap you may have specified.

.grid > .item {
    width: 23%;
    margin: 0 1%;
.grid {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr 1fr;
    column-gap: 1%;

A four column layout with squished columns
The width is now a percentage of the grid track — not the
container. (Large

Thankfully, there is a feature built into CSS and implemented
into modern browsers which helps us deal with this situation.
Feature Queries allow us to directly ask the browser what they
support and then act on the response. Just like a Media Query —
which tests for some properties of the device or screen — Feature
Queries test for support of a CSS property and value.

Test For Support

Testing for support is the simplest case, we use @supports and
then test for a CSS property and value. The content inside the
Feature Query will only run if the browser responds with true, i.e.
it does support the feature.

Test For No Support

You can ask the browser if it does not support a feature. In
this case, the code inside the Feature Query will only run if the
browser indicates it has no support.

@supports not (display: grid) {
    .item {
        /* CSS from browsers which do not support grid layout */

Test For Multiple Things

If you need more than one property to be supported, use and.

@supports (display: grid) and (shape-outside: circle()){
    .item {
        /* CSS from browsers which support grid and CSS shapes */

If you need support of one property or another, use or.

@supports (display: grid) or (display: flex){
    .item {
        /* CSS from browsers which support grid or flexbox */

Picking A Property And Value To Test For

You don’t need to test for every property you want to use —
just something which would indicate support for the features you
are planning to use. Therefore, if you want to use Grid Layout, you
might test for display: grid. In the future (and once subgrid
lands in browsers), you might need to be more specific
and test for subgrid functionality. In that case, you would test
for grid-template-columns: subgrid to get a true response from only
those browsers which had implemented subgrid support.

If we now return to our floated fallback example, we can see how
feature queries will sort it out for us. What we need to do is to
query the browser to find out if it supports grid layout. If it
does, we can set the width on the item back to auto and the margin
to 0.

.grid > .item {
    width: 23%;
    margin: 0 1%;
@supports(display: grid) {
    .grid {
        display: grid;
        grid-template-columns: 1fr 1fr 1fr 1fr;
        column-gap: 1%;
    .grid > .item {
        width: auto;
        margin: 0;

Note that while I have included all of the grid code inside my
feature query, I don’t need to. If a browser didn’t understand
the grid properties it would ignore them so they could safely be
outside of the feature query. The things that must be inside a
feature query in this example are the margin and width properties,
as these are needed for the old browser code but would also be
applied by supporting browsers.

Embrace The Cascade

A very simple way to offer fallbacks is to utilize the fact that
browsers ignore CSS that they don’t understand, and the fact that
where everything else has equal specificity, source order is taken
into account in terms of which CSS is applied to an element.

You first write your CSS for browsers which do not support the
feature. Then test for support of property you want to use, if the
browser confirms it has support overwrite the fallback code with
your new code.

This is pretty much the same procedure that you might use when
using media queries for responsive design, following a mobile-first
approach. In that approach, you start with your layout for smaller
screens, then add or overwrite things for larger ones as you move
up through your breakpoints.

Can I Use CSS Feature
Data on support for CSS Feature Queries across the
major browsers from caniuse.com.

The above way of working means that you do not need to worry
about browsers which do not support Feature Queries. As you can see
from Can I Use, Feature Queries have really great support. The
standout browsers that do not support them being any version of
Internet Explorer.

It is likely, however, that the new feature you want to use is
also not supported in IE. So, at the present time you will almost
always start by writing CSS for browsers without support, then you
test with a Feature Query. This Feature Query should test for

  1. Browsers which support Feature Queries will return true if they
    have support and so the code inside the query will be used,
    overwriting the code for older browsers.
  2. If the browser supports Feature Queries but not the feature
    being tested, it will return false. The code inside the feature
    query will be ignored.
  3. If the browser does not support Feature Queries then everything
    inside the Feature Query block will be ignored, which means that a
    browser such as IE11 will use your old browser code, which is very
    likely exactly what you want!

2. Dealing With Browser “Bugs”

The second browser support issue is thankfully becoming less
common. If you read “What
We Wished For
” (published at the end of last year), you can
get a little tour into some of the more baffling browser bugs of
the past. That said, any software is liable to have bugs, browsers
are no exception. And, if we add to that the fact that due to the
circular nature of specification implementation, sometimes a
browser implemented something and then the spec changed so they now
need to issue an update. Until that update ships, we might be in a
situation where browsers do something different to each other.

Feature Queries can’t help us if the browser reports support
of something supports it badly. There is no mode by which the
browser can say, “Yes, but you probably won’t like it.” When
an actual interoperability bug shows up, it is in these situations
where you might need to be a little more creative.

If you think you are seeing a bug then the first thing to do is
confirm that. Sometimes when we think we see buggy behavior, and
browsers doing different things, the fault lies with us. Perhaps we
have used some invalid syntax, or are trying to style malformed
HTML. In those cases, the browser will try to do something;
however, because you aren’t using the languages as they were
designed, each browser might cope in a different way. A quick check
that your HTML and CSS is valid is an excellent first step.

At that point, I’d probably do a quick search and see if my
issue was already widely understood. There are some repos of known
issues, e.g. Flexbugs and
However, even just a well-chosen few keywords can turn up Stack
Overflow posts or articles that cover the subject and may hand you
a workaround.

But let’s say you don’t really know what is causing the bug,
which makes it pretty hard to search for a solution. So, the next
step is to create a reduced test case of your issue, i.e. stripping
out anything irrelevant to help you identify exactly what triggers
the bug. If you think you have a CSS bug, can you remove any
JavaScript, or recreate the same styling outside of a framework? I
often use CodePen to pop together a reduced test case of something
I am seeing; this has the added advantage of giving me the code in
a way I can easily share with someone else if I need to ask about

Most of the time, once you have isolated the issue, it is
possible to think up an alternate way of achieving your desired
result. You will find that someone else has come up with a cunning
workaround, or you can post somewhere to ask for suggestions.

With that said, if you think you have a browser bug and can’t
find anyone else talking about the same issue, it is quite possible
you have found something new that should be reported. With all of
the new CSS that has landed recently, issues can sometimes show up
as people start to use things in combination with other parts of

Check out this post from Lea Verou about reporting such issues,
The Community! Report Browser Bugs!
”. The article also has
great tips for creating a reduced test case.

3. Partial Support Of CSS Properties

The third type of issue has become more common due to the way
that modern CSS specifications are designed. If we think about Grid
Layout and Flexbox, these specs both use the properties and values
in Box Alignment Level 3, to do alignment. Therefore, properties
such as align-items, justify-content, and column-gap are specified
to be used in both Grid and Flexbox as well as other layout

At the time of writing, however, the gap properties work in Grid
Layout in all grid-supporting browsers, and column-gap works in
Multicol; however, only Firefox has implemented these properties
for Flexbox.

If I were to use margins to create a fallback for Flexbox, then
test for column-gap and remove the margins, my boxes will have no
space between them in browsers which support column-gap in Grid or
multicol, so my fallback spacing will be removed.

@supports(column-gap: 20px) {
    .flex {
        margin: 0; /* almost everything supports column-gap so this will always remove the margins, even if we do not have gap support in flexbox. */

This is a current limitation of Feature Queries. We don’t have
a way to test for support of a feature in another feature. In the
above situation, what I want to ask the browser is, “Do you have
support for column-gap in Flexbox?” This way, I can get a
negative response so I can use my fallback.

There is a similar issue with the CSS fragmentation properties
break-before, break-after, and break-inside. As these have better
support when the page is printed, browsers will often claim
support. However, if you are testing for support in multicol, you
get what appear to be false positives. I’ve raised an
issue over at the CSS Working Group for this issue
, however, it
isn’t a straightforward problem to solve. If you have thoughts,
please do add them there.

Testing For Selector Support

Currently, Feature Queries can only test for CSS Properties and
Values. Another thing we might like to test for is the support of
newer selectors, such as those in Level 4 of the Selectors
specification. There is
an explainer note
and also an implementation behind a flag in
Firefox Nightly of a new feature for Feature Queries which will
achieve this.

If you visit about:config in Firefox and enable the flag
layout.css.supports-selector.enabled then you can test to see if
various selectors are supported. The syntax is currently very
straightforward, for example to test for the :has selector:

@supports selector(:has){
  .item {
      /* CSS for support of :has */

This is a specification in development, however, you can see how
features to help us manage the ever-present issues of browser
support are being added as we speak.

Further Reading

It can seem frustrating when you want to use a feature and
discover that it isn’t supported by one major browser, or if
things seem to be behaving in different ways. I’ve rounded up
some practical further reading that might help.

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