OK I opened a sand box and took a series of screen shots
First obsidian in light mode and a mermaid sequence diagram with no theme setting
Now switch obsidian to dark mode
Next add dark theme to mermaid diagram
Switch back to light mode in obsidian
Finally set mermaid theme to light
I suspect by default the mermaid diagrams are rendered with the mermaid light theme. Synchronising the mermaid theme used as the base theme for rendering diagrams with the obsidian theme would produce better visual appearance out of the box. It should still be possible to override parts of the theme locally if required.
The show debug info for the vault:
Sandbox vault
SYSTEM INFO:
- Obsidian version: v1.3.5
- Installer version: v1.3.5
- Operating system: Windows 10 Pro 10.0.22621
- Login status: logged in
- Catalyst license: none
- Insider build toggle: off
- Live preview: on
- Legacy editor: off
- Base theme: light
- Community theme: none
- Snippets enabled: 0
- Restricted mode: on
RECOMMENDATIONS:
- none