Thymeleaf guide
Thymeleaf is a Java XML/XHTML/HTML5 template engine that can work both in web (servlet-based) and non-web environments. It is better suited for serving XHTML/HTML5 at the view layer of MVC-based web applications, but it can process any XML file even in offline environments.
It is one of supported by Sping Boot template engines.
One of the advantages is that Thymeleaf mostly are used additional attributes, not tags. So you can check how look page in browser without deploing application.
<!DOCTYPE html>
<html th:lang="${pageData.content.lang}">
<head>
<meta charset="UTF-8">
<title>[[${pageData.content.title}]]</title>
</head>
<body>
<th:block th:replace="/content/fragments/top_header.html :: topHeaderDefault()"></th:block>
<div class="kcms-main flex-row">
<div class="kcms-left"></div>
<div class="kcms-center flex-grow-1 p-4 flex-column">
<article>
<h1 th:text="${pageData.content.title}" style="text-align: center;">default header</h1>
[(${pageData.content})]
</article>
</div>
<div class="kcms-right"> </div>
</div>
<footer></footer>
</body>
</html>