Supported inline styles wherever possible in Writer:
Strong <strong>
Emphasise <em>
Highlight <mark>
Anchor link <a>
Body elements
Article document format used by Writer is NewsML, a standard xml format. Body text use elements. Elements are rendered in Naviga Web with views/article/element.twig. You could override that in a child theme if you need to.
NewsML element
HTML element
Blockquote
<blockquote>
Headline
<h1 itemprop="name">
Subheadline
Subheadline [1-6]
<h2>
Body
<p class="ew_body">
Drophead
<p class="ew_drophead">
Preamble
<p class="ew_preamble" itemprop="description">
Ordered list
<div><ol><li>
Unordered list
<div><ul><li>
All other elements
<p>
Create your own article template
Articles are rendered with single-article.php, override that in your child theme to use own php code or twig.