!! Version 2

!! hooks
templatestyles
!! endhooks

!! functionhooks
invoke
!! endfunctionhooks

!! article
Template:TemplateStyles test/styles.css
!! text
.foo {
	color: red;
}
!! endarticle

!! article
Module:TemplateStyles test
!! text
local p = {}

function p.main()
	return mw.ext.TemplateStyles.link( 'Template:TemplateStyles test/styles.css' )
end

return p
!! endarticle

!! test
TemplateStyles Scribunto library loads styles
!! wikitext
{{#invoke:TemplateStyles test|main}}
!! html
<style data-mw-deduplicate="TemplateStyles:r11">.mw-parser-output .foo{color:red}</style>
!! end