Support extending the default style sheet

[micheljung]

From Extend the default stylesheet:

Now tell Asciidoctor to use your custom stylesheet instead of the default one:

asciidoctor -a stylesheet=my-asciidoctor.css document.adoc

Asciidoctor will now embed the contents of your custom stylesheet instead of the default one. However, Asciidoctor will not embed the contents of the default stylesheet. Instead, the browser will fetch it from the location specified by the @import directive. You can avoid this network call by putting the default stylesheet in the same directory as your custom stylesheet and linking to it using @import "asciidoctor.css".

However, if you put asciidoctor.css next to your stylesheet, the plugin will not copy it to build/docs/asciidoc thus it is not accessible by the browser.

[micheljung]

This solves the issue:

tasks {
tasks {
  "asciidoctor"(org.asciidoctor.gradle.jvm.AsciidoctorTask::class) {
    setBaseDir(sourceDir)

    resources(delegateClosureOf<CopySpec> {
      from("src/docs/asciidoc/style") {
        include("*.css")
        exclude("my-asciidoctor.css")
      }

      into("./")
    })

    attributes(
      mapOf(
        "stylesdir" to "style",
        "stylesheet" to "my-asciidoctor.css",
      ),
    )
  }
}