A small tip for those using custom:expander-card in Home Assistant. The title-field doesn’t support formatting, it seems. But you can solve this using the title-card property.

Before:

After:

Code example:

type: custom:expander-card
padding: 0
clear: true
title-card-button-overlay: true
title-card-clickable: true
expanded: false
title-card:
  type: markdown
  content: "**Example title**"
cards:
...