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@title CSS Coding Standards
@group standards
This document describes CSS features and coding standards for Phabricator.
= Overview =
This document describes technical and style guidelines for writing CSS in
Phabricator.
Phabricator has a limited CSS preprocessor. This document describes the features
it makes available.
= Z-Indexes =
You should put all `z-index` rules in `z-index.css`, and keep them sorted. The
goal is to make indexes relatively manageable and reduce the escalation of the
Great Z-Index War where all indexes grow without bound in an endless arms race.
= Color Variables =
Phabricator's preprocessor provides some standard color variables. You can
reference these with `{$color}`. For example:
lang=css
span.critical {
color: {$red};
}
You can find a list of all available colors in the **UIExamples** application.
= Printable Rules =
If you preface a rule with `!print`, it will be transformed into a print rule
and activated when the user is printing the page or viewing a printable version
of the page:
lang=css
!print div.menu {
display: none;
}
Specifically, this directive causes two copies of the rule to be written out.
The output will look something like this:
lang=css
.printable div.menu {
display: none;
}
@media print {
div.menu {
display: none;
}
}
The former will activate when users look at the printable versions of pages, by
adding `__print__` to the URI. The latter will be activated in print contexts
by the media query.
= Device Rules =
Phabricator's environment defines several device classes which can be used to
adjust behavior responsively. In particular:
lang=css
.device-phone {
/* Smallest breakpoint, usually for phones. */
}
.device-tablet {
/* Middle breakpoint, usually for tablets. */
}
.device-desktop {
/* Largest breakpoint, usually for desktops. */
}
Since many rules are specific to handheld devices, the `.device` class selects
either tablets or phones:
lang=css
.device {
/* Phone or tablet (not desktop). */
}
= Image Inlining =
Phabricator's CSS preprocessor automatically inlines images which are less than
32KB using `data:` URIs. This is primarily useful for gradients or textures
which are small and difficult to sprite.

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