Skip to content

Writing UserCSS

tophf edited this page Nov 21, 2021 · 7 revisions


It's a standard userstyle, optionally self-hosted, with metadata in a /* comment */ at the beginning, where you can enable various advanced features like preprocessor and user-customizable variables, which can be switched on the fly in the built-in config UI, for example:

Configuration screenshot of advanced UserCSS example

View example source
/* ==UserStyle==
@name         Stack Overflow Navbar Enhancer
@description  Move navbar position, change font color, and more.
@namespace    eight04.blogspot
@version      0.1.8
@author       eight04 <> (
@license      unlicense
@preprocessor stylus

@var          color    fontColor "Font color"    #123456
@var          select   navPos    "Navbar position" {
    "Top": "top",
    "Bottom": "bottom"
@var          checkbox fixNav    "Fixed navbar"  1
@var          text     navHeight "Navbar height" 60px
==/UserStyle== */

@-moz-document domain("") {
  body {
    color: fontColor;
    background: #eee;
  if navPos == "bottom" {
    body > .container {
      padding-top: 0 !important;
    body > footer {
      padding-bottom: 60px !important;
    body > header {
      top: auto !important;
      bottom: 0 !important;
  if not fixNav {
    body {
      position: relative !important;
    body > header {
      position: absolute !important;
  body > header {
    height: navHeight !important;

Table of Contents


Initial installation and live reload

With the Stylus extension enabled in your browser, open any {name}.user.css file (Firefox: Ctrl or + O) and it will automatically open a new browser tab with the UserCSS ready for installation, along with a few options:

  • An "Install" button will be available in the top left corner. Click to install the UserCSS.
  • A checked checkbox with "Install update from ..." will be shown. This indicates that when the extension checks for updates, it will use the URL provided to determine if an update is available.
  • A "Live reload" checkbox is shown if installing a UserCSS from a local source (file:///...) and also localhost in the upcoming version of Stylus.
    • If checked, after installation, the style within the installation tab will update automatically when the local file is altered elsewhere.
    • If you had Stylus' built-in editor opened for this style, which you don't need to use the live reload feature, a confirmation will be shown if the local file has been altered and the style is unsaved in the built-in editor. Normally you wouldn't need to open the editor when using live reload, so this warning is just there to prevent the loss of changes you may have made in the built-in editor.
    • While editing a UserCSS locally, any issues within the UserCSS will be shown on the installation page; you may have to switch tabs to see these messages if the browser editor style isn't updating as expected.
    • The live reload ability is lost when the installation page is closed.
    • Note that you must give Stylus extra permission to make live reload work in Chrome: Extensions > Stylus Details > Enable "Allow access to file URLs".


Opening a UserCSS a second time will reveal a "Reinstall" button. Click to reinstall the UserCSS.

A disabled checked checkbox with "Install update from ..." will be shown. This indicates that the installed style is from the same source.

A warning will be displayed if the UserCSS is an older version of the one that is currently installed.


On the Manage page ("Installed Styles") each UserCSS entry will include one or more of the following icons:

Screenshot of the open homepage, delete, check for update, and configure buttons

In order from left to right, they represent:

  • External link pointing to the source page.
    • Derived from the @homepageURL setting.
    • Hovering over the icon will show the URL in the tooltip.
    • This icon will not be present if no @homepageURL was defined.
  • Delete style.
  • Update style:
    • This checks the URL from where it was installed.
    • If the "Install update from ..." checkbox was left unchecked during installation, this icon will not be present.
  • UserCSS configuration (see the next section).


To configure a UserCSS, go to the Manage page and click on the "Configure" icon (Gear icon seen in the screenshot above) to open the dialog.

The contents of the configure dialog depend on the UserCSS @var type settings:

  • text - A plain text input is provided.
  • color - A color type input is shown along with a slider to set the opacity.
  • checkbox - A checkbox will be provided; it is styled as a sliding switch.
  • select - A dropdown select with preset options will be provided.
  • number - A plain number input is provided (added in Stylus v1.4.23).
  • range - A plain range slider is provided along with the current value and any units (if set) (added in Stylus v1.4.23).

Make the desired changes and click:

  • "Save" to save your current selections.
  • "Reset" to reset the configuration to the default settings.
  • "Close" to close the popup.


To create a UserCSS format style:

  • From the Manage page, check the "as UserCSS" checkbox next to the "Write new style" button.
  • Click on the "Write new style" button.
  • A basic UserCSS template will then be available.

Change default template

  • To change the default UserCSS template, create a UserCSS style as described above.
  • Within the default template, make any changes to the template to suit your needs.
  • Clear the @name meta entry. Make it blank after the @name.
  • Click the "Save" button (or use Ctrl or + s).
  • A confirmation dialog will appear asking if you want to replace the current template, click "Yes".
  • The next time the "Write new style" UserCSS template it used, the modified template will be used.


All UserCSS styles require the following metadata entries:

  • @name
  • @version
  • @namespace
  • @license (not required, but essential if you want to share your work)

See the full list of supported UserCSS metadata below.

Choose a preprocessor

The @preprocessor setting will determine how the code will be compiled and therefore what "CSS flavour" you use. These preprocessors can extend the standard CSS syntax by lots of convenient features. It is important to follow the syntax of the preprocessor you picked:

Pure SASS external link syntax is currently not supported.


If enabled, the CSS linter will automatically switch to use stylelint. This is because stylelint supports a "sugarss" syntax external link, which closely approximates the Stylus language. However, stylelint does not correctly report all issues in the Stylus language format because of minor differences between the syntax.

Applies to

  • Add additional entries by:
    • Typing any supported @-moz-document external link matching function within the editor.
    • Or, clicking an "Add" button within the "Applies to" section.
  • Remove entries by:
    • Deleting the @-moz-document matching function within the editor.
    • Or, clicking on the "Remove" button within the "Applies to" section. The last entry will not be removed.

Note: The documentation for @document reports that it is currently only supported in Firefox external link and must include a -moz prefix. This is why we always refer to it as @-moz-document within this document.

Hosting a UserCSS

When linking to the .user.css file, you'll need to link to the "raw" version of the style.

  • GitHub Repo:{USER}/{REPO}/master/{NAME}.user.css
  • Raw.GitHack:{USER}/{REPO}/master/{NAME}.user.css
  • GitCDN:{USER}/{REPO}/master/{NAME}.user.css
  • Bitbucket:{USER}/{REPO}/raw/HEAD/{NAME}.user.css
  • GitLab:{USER}/{REPO}/raw/master/{NAME}.user.css
  • GitHub Gist:{USER}/{SHA}/raw/{REVISION-SHA}/{NAME}.user.css
    Remove the {REVISION-SHA} to get the latest version.
  • Dropbox:{RANDOM}/{NAME}.user.css?dl=0
    Modify the public share link by changing the subdomain from www to dl and adding ?dl=0 to the end.

Special case:

If the linked file doesn't end in .user.css or .user.css? with parameters you have to add a dummy parameter like ?dummy=.user.css to the end of the URL:

  • GitLab Snippets:{USER}/{REPO}/snippets/{ID}/raw?dummy=.user.css


Add a badge to let users know your style can be installed directly

  • [![Install directly with Stylus](](MY.USER.CSS)

  • [![Install directly with Stylus](](MY.USER.CSS)

  • [![Install directly with Stylus](](MY.USER.CSS)

Replace MY.USER.CSS with a direct link to your style in user.css format (e.g. GitHub's raw URL -{user}/{repo}/master/my-style.user.css).

Don't forget that the file must end in .user.css otherwise Stylus won't recognize it as such.


For general help on editing, see Writing styles.

Usercss Metadata


The name of your UserCSS style. Mandatory.
The combination of @name and @namespace must be unique for each UserCSS.

Leave @name empty to create a template for new UserCSS styles.


@name example site awesome dark


The namespace of the UserCSS. Mandatory.
Helps to distinguish between styles with the same name. Usually, the author's nickname or homepage. Can contain spaces and special characters.

The combination of @name and @namespace must be unique for each UserCSS.




The version of your style. Mandatory.
This is used for the update check.

Follow semver external link versioning for maximum compatibility with other extensions or style-processing utilities.

If you use Stylus 1.5.18 or newer, @version can contain any amount of dot-separated digits and CalVer (calendar versioning) with its 0-padded numbers.


@version 1.0.0


A short significant description.


@description A UserCSS style to make people happy


Info about the author of the UserCSS style.

Order of parameters is compulsory: name [<email optional>] [(URL optional)].

If an email address is included (wrapped in angle brackets), it will be shown as a "mailto" link on the install page.

If a URL is included (wrapped in parentheses), it will be shown as an external link on the install page.


@author My Name <> (


The project's homepage that is used in Stylus' Manage and Edit pages to link to UserCSS source.
This is not an update URL. The update path is the URL the UserCSS was installed from.




The URL the user can report issues to the UserCSS author. Displayed as "Feedback" link in the style's UserCSS configuration popup.




When defined, this URL is used when updating the style otherwise the style is updated from where it was installed.




Include a license based on the SPDX license identifier external link. Essential.


@license CC-BY-SA-4.0

If no license external link is included, it will be assumed that no one can use, copy, distribute, or modify the work.


Applies a CSS preprocessor.
The preprocessors listed below are supported.


The default mode with standard CSS syntax external link is used if

  • @preprocessor default is set or
  • @preprocessor is missing and no variable is defined by @var or @advanced.

With the default preprocessor set, UserCSS variable definitions like

@preprocessor default
@var text  myFontSize        "Font size"        16px
@var color myBackgroundColor "Background color" #0b0

will generate a variable list, which is concatenated to each section of the style:

:root {
  --myFontSize: 16px;
  --myBackgroundColor: #0b0;


This mode inspired by the syntax external link is used if

  • @preprocessor uso is set or
  • @preprocessor is missing and there are variables defined by @var or @advanced.

In addition to standard CSS features, placeholders external link (/*[[variable-name]]*/) will be replaced with their values recursively.


The UserCSS will be compiled following the less syntax external link.


This setting will use the Stylus-language preprocessor on the UserCSS.

  • Please refer to the Stylus-lang documentation external link for more details about Stylus' selectors, variables, interpolation, operators, etc.
  • Note that Stylus-language is aware of indents and can be written without any brackets. This might cause errors if you are relying on brackets only. However, always pay attention to proper indentation.
  • Known pitfall: Stylus-lang replaces the known url() with its own function external link so if you want to use base64-encoded data-URIs external link, you need to declare it as literal CSS external link.
  • Also be aware that not all functionality may be available, such as @import, @require and @font-face.

The UserCSS variable definition

@var text myFontSize "Select a font size" 14px

will be compiled to a Stylus-lang definition

myFontSize = 14px

which is then concatenated to the source code and compiled with Stylus-lang.


Defines a live-switchable variable which will be compiled to valid CSS according to the preprocessor that is set.

@var is interchangeable with @advanced (used by xStyle).

The @var includes the following properties in this order:

@var <type> <name> <label> <default value>

All properties are required, but for the select type some can be combined if they're the same.


@var <type> <name>   <label>        <default value> */
@var text   myBorder "Border style" 3px dotted blue

Do not include the keyword !important into the variable value.

Within the style, refer to the above variable as follows:


Choose one of these types to be used within the configuration menu

  • text - Provides a plain text input.
  • color - Provides color type input with alpha slider.
  • checkbox - Provides a checkbox styled as slide switch.
  • select - Provides a select element (same as dropdown and image types provided by xStyle).
  • range - Provides a range slider with the current value, and any units, displayed (added in Stylus v1.4.23).
  • number - Provides a plain number type input element with user input clamped to any min, max or step values (added in Stylus v1.4.23).


The name of the variable. Must match regular expression /[\w-]+/ which means letters (small and caps), numbers, _ and -.


The label describing a variable shown in the configuration popup. Must be enclosed with quotes (' or ") if the string contains spaces or special characters.

default value

The default value for the variable. Having a default value is mandatory.

  • text - Include a string value.
    If the string contains a colon (:), wrapping in single quotes and additional wrapping in double quotes is required.
  • color - Use a hex (3, 4, 6 or 8-digit hex codes), rgb or rgba color.
  • checkbox - Set 1 for checked or 0 for unchecked.
  • range - Include an array of values (added in Stylus v1.4.23):
    • Set as [default, min, max, step, units].
    • All items but the default value are optional.
    • The default, min, max and step values must be numeric (or null), or it will cause a parsing error.
    • Values set to null are ignored.
    • The units value - framed in (double)quotes - may be added in at any position since it's non-numeric; but the default, min, max and step values are set in order, e.g. ['px', 5, 0, 10, 1], [5, 0, 'px', 10, 1] or [5, 0, 10, 'px', 1], etc, will all set the default to 5, min to 0, max to 10, step to 1 and the units to px.
    • Only the first units value entry will be used, any additional (non numeric) entries will be ignored, e.g. [5, 0, 10, 1, 'px', 'em'] will only set the units to px. The em entry is removed.
    • because we're parsing the meta data as JSON, all fractional values must include an integer value, e.g. [.5] will cause a parse error, so use [0.5]
    • this variable option is not (yet) supported by other userstyle managers, so please make sure your users are aware of this fact.
  • number - Same as range (added in Stylus v1.4.23). The only difference is that a plain number type input is rendered.
  • select
    • Use a JSON format for the values set in the select's options.
    • Each key:value pair represents an option.
    • Default options can be indicated by adding an asterisk to the end of the key name (added in Stylus v1.4.23), e.g.
      • ["Arial", "Consolas*", "Times New Roman"] ("Consolas" will be set as the default).
      • "nearWhite*": "#ddd" ("nearWhite" is set as the default).
      • "near_white*:Near White": "#ddd" ("near_white" is set as the default).
    • The key is composed with OPTION_NAME:OPTION_LABEL. Option names must be unique from each other:
      @var select fontBkgd "Background" {
        "near_black:Near Black": "#222",
        "near_white:Near White": "#ddd"
    • If the option name, label, and value are the same, it can be shortened to an array. For example:
      /* ...
      @preprocessor stylus
      @var select fontName "Font name" ["Arial", "Consolas", "Times New Roman"]
      ... */
      @-moz-document domain("") {
        body {
          font-family: fontName !important;
    • If the value equals the name, it can be shortened to an array. For example:
      /* ...
      @preprocessor stylus
      @var select theme "Theme" ["dark:Dark theme", "light:Light theme"]
      ... */
      @-moz-document domain("") {
        body {
          if theme == dark {
          } else if theme == light {
    • Option name can be omitted:
      @var select fontBkgd "Background" {
        "Near Black": "#111",
        "Near White": "#eee"
      In this case, the option name (key) is used as option label.

Settings will be kept during updates if the option names / option keys don't change.

Use backtick (`) to enclose multi-line string.

Variable examples

/* ==UserStyle==
@name         test
@description  UserCSS example
@author       me
@version      0.1.0
@preprocessor stylus
@var checkbox fontEnable "Font enabled" 1
@var text     fontSize   "Font size"    2.1em
@var color    fontColor  "Font color"   #123456
@var select   fontName   "Font name"    ["Arial", "Consolas*", "Times New Roman"]
@var select   fontBkgd   "Body background color"   {
  "Near Black": "#111111",
  "Near White*": "#eeeeee"
@var text     bkgdImg    "Bkgd image"   "''"
@var text     logoImg    "Logo image"   none
@var number   adOpacity  "Ad opacity"       [0.5, 0, 1, 0.1]
@var range    imgHeight  "Max image height" [50, 10, 200, 10, "px"]
==/UserStyle== */
@-moz-document domain("") {
  if font-enable {
    body {
      font-size: fontSize !important;
      color: fontColor !important;
      font-family: fontName !important; /* Consolas (without the "*") will be set as default */
      background-color: fontBkgd !important;
      /* This approach will not allow setting the background-image to "none" */
      background-image: url(bkgdImg) !important;
    #logo {
       /* This approach will, but needs url('URL_HERE') written in the config input if set to a URL */
      background-image: logoImg !important;
    #ad {
      opacity: adOpacity !important;
    img {
      max-height: imgHeight !important; /* the 'px' is added to this value automatically */

xStyle compatibility

The xStyle extension external link also provides UserCSS metadata which differs slightly from our specification.

If writing a new style, make sure to set the @preprocessor appropriately. At the time of this writing, the Stylus language preprocessor is not supported by xStyle.

Our implementation supports use of:

  • @preprocessor must be either undefined or set to uso in the metadata.
    • The UserCSS placeholder (/*[[my-variable]]*/) must be used to reference @advanced variable names.
  • @advanced interchangeable with our @var definition.
  • dropdown external link type - Supported but use of <<<EOT and EOT; is required.
  • image external link types - supported

For more details, see the xStyle options external link documentation.

xStyle Example:

/* ==UserStyle==
@name      test
@namespace tester
@version   0.1.0
@license   unlicense

@advanced  text     a_text       "A Text"  "SomeWords"
@advanced  color    a_color      "A Color" #ffffff;
@advanced  dropdown a_background "Your browser" {
  fx "Firefox" <<<EOT
background-color: red; EOT;
  cr "Chrome" <<<EOT
background-color: green; EOT;
@advanced  image    a_background_image "Page background" {
  bg_1 "Background 1" ""
  bg_2 "Background 2" ""
==/UserStyle== */

@-moz-document domain("") {
  div.message::after {
    content: /*[[a_text]]*/;
  div.message {
    color: /*[[a_color]]*/
    background-image: url(/*[[a_background_image]]*/);

More examples

The settings on allow users to choose a default image or set a custom image. To realize this in UserCSS, a tricky combination of select and text is used:

  • Using @var
/* ==UserStyle==
@name         Background image
@description  How to add a default & custom background image
@namespace    examples
@version      0.1.0
@preprocessor default
@var select bg-selected "Background image" {
 "Default image 1": "url(",
 "Default image 2": "url(",
 "Custom": "var(--bg-custom, none)",
 "None": "none"
@var text bg-custom "Custom Background; include url()" "url()"
==/UserStyle== */

@-moz-document domain("") {
  body {
    background-color: #222 !important;
    background-image: var(--bg-selected) !important;
  • The same using @advanced:
/* ==UserStyle==
@name        Background image
@description How to add a default & custom background image
@namespace   examples
@version     0.1.0
@advanced dropdown bg-selected "Background image" {
 image1 "Default image 1" <<<EOT
 url( EOT;
 image2 "Default image 2" <<<EOT
 url( EOT;
 custom "Custom background" <<<EOT
 var(--bg-custom, none) EOT;
 noBG "None" <<<EOT
 none EOT;
@advanced text bg-custom "Custom Background; include url()" "url()"
==/UserStyle== */

@-moz-document domain("") {
  :root {
    --bg-custom: /*[[bg-custom]]*/;
  body {
    background-color: #222 !important;
    background-image: /*[[bg-selected]]*/ !important;