Wikipedia:TemplateStyles

TemplateStyles allow custom CSS pages to be used to style content without an interface administrator having to edit sitewide CSS. TemplateStyles make it more convenient for editors to style templates; for example, those templates for which the sitewide CSS for the mobile skin or another skin (e.g. Timeless) currently negatively affects the display of the template.

TemplateStyles work on all types of pages, not just templates, despite the name.

Guidelines
Note that the Manual of Style, including the Accessibility guidelines, still applies.
 * The style must apply only to the associated template's output. It may also apply to highly-relevant nearby wikitext where the template is used. (For example, there are many table templates which should have TemplateStyles which are provided entirely in templates, or which may provide a legend to a wikitext table.) It would otherwise be confusing if adding a template to one part of a page were to completely or partially change the display or styling of an unrelated part of the page.
 * Style pages should be associated with a specific template or group of templates, and named accordingly. This allows style pages to be easily identified and edited. In general, this means that a style page should be a subpage of the related template, e.g.: Template:myTemplate/styles.css or Template:myTemplate/styles-foo.css, but not Template:styles-foo.css nor Template:foo.css.
 * Generally follow the MediaWiki coding conventions for CSS. Some specifics:
 * Use selectors that are highly likely to be unique to the template being used. This reduces the chance of conflicting CSS rules arising accidentally. Examples: Use .myTemplate-row rather than .row or .myTemplate tr rather than tr.
 * Avoid using #id per the conventions. HTML IDs are supposed to be unique on a page. Templates are rarely used uniquely, and those that are initially single-use-per-page are often later used in unanticipated ways. Use classes instead of IDs for styling.
 * Avoid using !important per the conventions, except in mobile views to override style input from the associated template. Use of  in TemplateStyles is exceptionally difficult to override because of loading order of styles (personal CSS then TemplateStyles).
 * In templates intended to be substituted, or those likely to be substituted, use ifsubst to remove the TemplateStyles tag. Example: allcaps.
 * Inline styles may be used as the "if substed" case in a substituted template. Example: smallcaps.
 * Images that do not require attribution (i.e. those in the public domain) are the only images that may be used as background images. For normal file usage, attribution is provided on the file description page, accessed by clicking the image. This is not possible if the image is being used as the background.
 * The protection level of style pages should match that of their associated template. If a template is high-risk, then its styles are also high-risk, and should have the same protection. If a template is not high-risk, then vandalism to cause chaos could be achieved just by editing the template itself. A higher protection level for the style page would encourage editors to add inline styles to the template, since the template would be editable but the style page would not. Any templates using CSS pages with the wrong protection level will be categorized in.
 * Remember to add  to any protected CSS pages to ensure that they display the appropriate lock icon. Protected templates using CSS pages that lack the lock icon will be categorized in.

Workflow for conversion

 * 1) In Template:myTemplate, identify all of the inline styles that can be moved to a separate stylesheet.
 * 2) Create Template:myTemplate/styles.css containing all the classes that will replace the inline styles. Use template-specific class names where possible.
 * 3) In Template:myTemplate (or its Template:myTemplate/sandbox if you want to test first), add  (you don't need to specify the Template: namespace). It's probably best at the top so that it is obvious and to avoid a flash of unstyled content, but it will need to be on its own line if the template begins with wiki markup that has to start on a new line (e.g. wiki-table).
 * 4) Amend the template (or sandbox) to replace the inline styles with the classes you defined in Template:myTemplate/styles.css
 * 5) Do as much checking as you can. If you tested in the sandbox you can check the testcases page where it exists, but specifically check that the styles you affected render properly.
 * 6) Specifically, for templates meant to be used inline, check to see if there are uses inside of links. TemplateStyles templates will not work inside links (right now).
 * 7) If you used the sandbox, either make an edit request for the main template or do the update if you are confident of your changes.
 * 8) Request or amend the protection level of Template:myTemplate/styles.css to match that of Template:myTemplate as necessary.
 * 9) Add  to the template's documentation to show which TemplateStyles stylesheets it uses.

Tips

 * Uses of TemplateStyles stylesheets are recorded just like template transclusion and Scribunto module invocation. Special:WhatLinksHere and the "Templates used in this preview" section beneath the edit form will work for them in the usual manner.
 * To search for TemplateStyles stylesheets, you can search for . See also mw:Help:CirrusSearch.
 * When is placed on a template's documentation, it adds the template to Category:Templates using TemplateStyles. If the TemplateStyles stylesheet has a lower protection level, the template will be tracked in Category:Templates using TemplateStyles with a different protection level ( page).
 * TemplateStyles experiments can be created at Template:TemplateStyles sandbox, e.g. for use in Module:Sandbox module experiments.
 * TemplateStyles pages can be created outside of the template or module namespaces by either first creating them in template namespace and moving them (perhaps at Template:TemplateStyles sandbox), or by using Special:ChangeContentModel as an admin and template editor. Regardless of what method is used, creating a .css page in userspace can only be done by the user in question or an interface admin, but once it is created anyone can edit it.
 * Moving a sanitized CSS page will not create a redirect.

Overriding TemplateStyles
Because of the way TemplateStyles is implemented, overriding TemplateStyles in your personal CSS requires a little more effort than normal. The rules on a specific TemplateStyles sheet are not the full CSS rules, nor can you match the selectors to override them.


 * 1) Each selector is 'hoisted' to , so to override a rule in a TemplateStyles sheet that looks like  , a naive override in your personal CSS file would need to look like.
 * 2) However, in the HTML each TemplateStyles style is  placed after your personal CSS file loads. Accordingly, the new rule would need to be more specific. That can come in a couple ways. The easiest is to select the HTML element also as in:  . Another way would be to double one of the class selectors, as in   or  . This latter way is a little more future-proof but looks a little weirder.
 * 3) Lastly,   can always override styles in your personal CSS. The usual caveats regarding   apply. Prefer one of the two options in bullet two if possible. (You must do this to override inline styles, regardless of any of the above; some templates cannot move everything to TemplateStyles per the flexibility given to template users. Implementers of templates should consider whether parameters like   and   are actually necessary. See also phab:T200632.)

Examples

 * mw:Help:TemplateStyles/examples
 * mw:Template:Stylish (CSS)
 * mw:Template:ResponsiveAmboxExample (CSS)
 * Template:Thermometer and Template:Thermometer/styles.css give a simple demonstration of how TemplateStyles may be mixed with inline styles (where a parameter is passed to change one or more styles)