A post has an article header overlay with a solid background color (#123) in immersive mode with a translucent header.
front matter:
---
layout: article
title: Page - Article Header Overlay Background Fill (Immersive + Translucent Header)
mode: immersive
header:
theme: dark
article_header:
type: overlay
theme: dark
background_color: '#123'
background_image: false
---