The idea of Thymeleaf is to have valid HTML source code that even may contain sample data.
It uses special attributes for example th:… to that are getting picked up by the engine
Template
As your default layout put a default.html inside of src/templates
src/templates/default.html
<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<body>
<p>This is my website</p>
<div th:insert="${content} :: #content">
</body>The template engine processes every output of your content (asciidoc files)
The ${content} reflects the output of one asciidoc file (have a look at build/content)
Gradle Task
The Gradle task generateHTML processes all outputs of your content files.
Currently every file <name>.adoc will result in a build/pages/<name>/index.html. Except index.adoc files, they will stay on the same level.