Custom properties (--*): CSS variables - CSS: Cascading Style Sheets
color); } #secondparagraph { background-color: var(--second-color); color: var(--first-color); } #container { --first-color: #48ff32; } #thirdparagraph { background-color: var(--first-color); color: var(--second-color); } result specifications specification status comment css custom properties for cascading variables module level 1the definition of '--*' in that specification.

Writing JavaScript for XHTML - Archive of obsolete content
//--><!]]></script> <!-- (for styles, it is different) --> <style type="text/css"><!--/*--><![cdata[/*><!--*/ ...

CSS Custom Properties for Cascading Variables - CSS: Cascading Style Sheets
css properties --* specifications specification status comment css custom properties for cascading variables module level 1 candidate recommendation initial definition ...

CSS reference - CSS: Cascading Style Sheets
on-propertytransition-timing-functiontranslatetranslate()translate3d()translatex()translatey()translatez()turnuunicode-bidiunicode-range (@font-face)unset<url>url()user-zoom (@viewport)v:validvar()vertical-alignvh@viewportviewport-fit (@viewport)visibility:visitedvmaxvminvwwwhite-spacewidowswidthwidth (@viewport)will-changeword-breakword-spacingword-wrapwriting-modexxzz-indexzoom (@viewport)others--* selectors the following are the various selectors, which allow styles to be conditional based on various features of elements within the dom.