TiddlyWiki supports the usual HTML style attribute for assigning CSS styles to elements:

<div style="color:red;">Hello</div>

Introduced in v5.2.2 In an extension to HTML, TiddlyWiki also supports accessing individual CSS styles as independent attributes. For example:

<div style.color="red">Hello</div>

The advantage of this syntax is that it simplifies assigning computed values to CSS styles. For example:

<div style.color={{!!color}}>Hello</div>

New in v5.3.6 TiddlyWiki also supports setting CSS custom properties as independent attributes. For example:

<div --bg-color={{{ [[red]] }}}>Hello</div>