Style variables
What is a style variable?
A style variable represents a value shared across all of XWiki's style sheets. These values are meant to be used instead of hard-coding them in stylesheets. Our CSS codestyle makes the use of these variables mandatory in XWiki Standard development. It's recommended to rely on those for your own custom developments too 
They provide some level of consistency in the UI:
- It will be harder for customizations to have unwanted effects
- XWiki can provide colors that work well together by default. Among other things, it can help make sure all your components respect some minimum contrast.
- It's straightforward for your custom development components to be compatible with the color themes applied on multiple wikis
How to use style variables?
Currently, XWiki Standard with its Flamingo Skin supports three kinds of style variables. They are (ranging from the oldest to the newest):
- The old colorTheme variables
- The LESS variables (Flamingo colorTheme + design system inherited from bootstrap + Misc additions from the Flamingo skin)
- XWiki 17.3.0+ The CSS properties
All of these variables are supposed to be used in .css files, .less files and their respective StyleSheet Extensions's contents.
Using CSS properties XWiki 17.3.0+
Where are CSS properties declared?
XWiki standard CSS properties are declared in the file cssVariablesInit.css . Those variables from are still unstable and not documented here. Starting in XWiki 18, those variables should become stable and be documented with detail here.
CSS properties can also be declared pretty much anywhere in your custom stylesheets using standard CSS syntax
Use them in a CSS stylesheet
color: var(--brand-color);
}
Use them in a LESS stylesheet
color: ~"var(--brand-color)";
}
Developing with CSS properties
Using the macro defined in the page shared on this gist, you can easily view all the CSS variables available in your context:
New CSS properties
Those properties were introduced in XWiki 17.3.0+ and after. They are only available as CSS properties and do not have an equivalent in LESS variables.
| Since | Name | Type (from CSS) | Default value | Meaning |
| XWiki 17.3.0+ | 100vw | Size (vw) | 100vw | Part of a workaround to get a unitless screen width. |
| XWiki 17.3.0+ | int-viewport-width | Size (unitless) | Unitless screen width, useful for ratio calculations. | |
| XWiki 17.3.0+ | font-weight-regular | Number | 400 | Font weight used for regular text in the interface. |
| XWiki 17.3.0+ | font-weight-semibold | Number | 700 | Font weight used for semibold text in the interface. |
| XWiki 17.3.0+ | font-weight-bold | Number | 900 | Font weight used for bold text in the interface. |
LESS variables
Where are LESS variables declared?
XWiki Standard has its LESS variables declared in a few files, mostly:
- variables.less from the bootstrap module: pretty much everything to make the Bootstrap 3 design system work.
- variables.less from the flamingo module: XWiki's special variables and overrides for default values
- variablesInit.vm from the flamingo module:
- The flamingo Color Themes, those variables can be viewed and edited directly in the Administrator UI but they do not cover everything in the skin.
LESS variables can also be declared in any of your custom LESS stylesheets. If you can't find it in the xwiki-platform codebase, it's probably from a customization
Use them in a CSS stylesheet
Use them in a LESS stylesheet
color: @brand-color;
}
Old colorTheme variables
Use them in a CSS stylesheet
Make sure the content of your stylesheet is parsed. This will allow the use of Velocity Templating Language (VTL) in your stylesheet. The old colorTheme do rely on VTL to work properly. You also need to make sure you import the declaration of the variables done in the colorThemeInit.vm template so that your stylesheet compiles to a consistent result in any context.
#template('colorThemeInit.vm')
.box.box-custom {
color: $theme.textPrimaryColor;
}
Learn more about the old color theme variables
Really don't use them in a LESS stylesheet!
Make sure the content of your stylesheet is parsed. This will allow the use of Velocity Templating Language (VTL) in your stylesheet. The old colorTheme do rely on VTL to work properly. You also need to make sure you import the declaration of the variables done in the colorThemeInit.vm template so that your stylesheet compiles to a consistent result in any context.
.box.box-custom {
color: $theme.textPrimaryColor;
}
Migrating from LESS to CSS properties
This section contains a few points that could be important when migrating LESS styles to using the CSS properties. Those are not community rules to be followed, but just indications to make it easier to migrate
Syntax sugar
Native CSS is a bit more wordy than LESS:
- Variables start with a double dash (--) instead of an arobase (@)
- All use of a CSS variable should be made in a var block.
- All operations that you could write in your LESS must be made in a calc block.
--popover-arrow-color: var(--popover-bg);
--popover-arrow-outer-width: calc(var(--popover-arrow-width) + 1px);
}
Units in CSS calculus
LESS doesn't have any clearly defined unit system. CSS has a very strict unit system (some improvements to make it a bit looser and easier to use are discussed though). If a formula doesn't work in CSS, it's probably because the units do not respect the constraint of the operators:
- Addition and substraction, both values must have the same unit
- Multiplications and divisions, only one value has an unit, the second one is unitless.
The exact rules are more precise than that.
Migrating color functions
To migrate LESS color functions, you can use the CSS color or hsl functions:
--popover-bg: hsl(from var(--well-bg) h s calc(l - 0.07));
}
HSL is useful for most operations, color is really only useful for transparency calculations.
LESS color functions work directly with additions: darken(@well-bg, 7%) is the same as the snippet above. This is slightly different from calc( l * (1-0.07)) which was how I assumed LESS handled its operations at first.
Using CSS variables in LESS
Sometimes you want to start migrating a file without being able to move it all at once. In this kind of situation, you'll need to know about how to use CSS variables in a LESS file.
The LESS parser we use in XWiki standard is not maintained enough to ensure a good compatibility with current CSS. It does not work well with CSS variables directly. The usual solution to escape things in LESS works well for most cases: a tilde and the escaped content in between quotes.
-/**/-navbar-default-bg: ~"var(--brand-primary)";
-/**/-navbar-default-border: ~"color-mix(in srgb, var(--navbar-default-bg), black 6.5%)";
}
But, a quirk of the parser is that this syntax does not work when we're trying to use it for an assignation. One hack that's not too bad looking that works for those variable assignations is to add an empty comment block in the middle. It prevents the LESS parser from associating the two dashes together and assume this is the end of an HTML comment. You can see this workaround in the example above.
Migrating from old colortheme variables to CSS variables
There is no "easy" way to do this kind of migration because the old colorTheme variables do not map 1 to 1 to CSS variables. You might want to check how they got mapped to LESS variables to get an idea of CSS properties that have similar values (or just use the CSS properties with the semantics corresponding to your situation ). Those oldColorTheme -> Less variables mappings are available in the variablesInit.vm template.
Once you removed all the old colortheme variables from your stylesheet, you can also remove the call to the colorThemeInit.vm template and don't need to parse it anymore.
