Mermaid Themes

Mermaid themes control the visual style of your Mermaid diagrams. With different themes, the same Mermaid diagram can look formal, minimal, hand-drawn, or presentation-ready. Mermaid Viewer lets you preview Mermaid themes instantly so you can choose the best diagram style for documentation, system architecture, or slides.

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What Are Mermaid Themes?

Mermaid themes define the colors, fonts, line styles, and overall appearance of a Mermaid diagram. They do not change the structure or logic of the diagram — only how it looks. Using the right Mermaid theme improves readability, visual clarity, and suitability for different use cases such as technical documentation, printed documents, or presentations.

Preview Mermaid Themes Online

Mermaid Viewer provides an online Mermaid theme preview experience. Paste your Mermaid code once and instantly switch between different themes to compare how each style looks. This makes it easy to experiment with Mermaid diagram styles without modifying your original diagram definition.

Available Mermaid Themes

Below are common Mermaid themes you can preview using Mermaid Viewer.

✏️ Excalidraw (Hand-drawn)

The Excalidraw-style Mermaid theme gives diagrams a hand-drawn, sketch-like appearance. Ideal for early-stage design discussions, brainstorming, and presentations where a less formal look feels more approachable.

Base (Customizable)

The base Mermaid theme is a customizable starting point. Use it when you want to align diagrams with brand guidelines or design systems.

Default

The default Mermaid theme provides a clean and balanced appearance suitable for general use in documentation and READMEs.

Neutral

The neutral Mermaid theme is optimized for print and formal documents, with restrained colors and clean lines for reports and PDFs.

Dark

The dark Mermaid theme is designed for dark backgrounds and dark-mode documentation, reducing eye strain and fitting developer tools.

Forest

Green-themed diagrams

How to Choose the Right Mermaid Theme

Different Mermaid themes work better for different scenarios:

Use hand-drawn themes for ideation and early design discussions
Use default or neutral themes for documentation and technical references
Use dark themes for dark-mode interfaces and developer-focused tools
Use customizable themes for branded or client-facing materials

Previewing Mermaid themes before exporting diagrams helps ensure your diagrams match their intended context.

Mermaid Themes for Common Use Cases

Mermaid themes are commonly used for:

System architecture diagrams
Software documentation and READMEs
Technical presentations and slides
Workflow and process diagrams
Design discussions and planning sessions

Mermaid Viewer helps you visually evaluate these themes before finalizing your diagrams.

Why Use Mermaid Viewer for Themes?

Mermaid Viewer is built specifically for previewing and comparing Mermaid themes. It focuses on styling and layout rather than diagram generation, making it a lightweight companion for anyone who already writes Mermaid code. By using Mermaid Viewer, you can quickly test how different Mermaid themes affect the look and readability of your diagrams.

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Frequently Asked Questions

What are Mermaid themes?

Mermaid themes define the visual appearance of Mermaid diagrams, including colors, fonts, and line styles.

Can I preview Mermaid themes online?

Yes. Mermaid Viewer lets you preview different Mermaid themes using the same Mermaid code, so you can compare styles instantly.

Do Mermaid themes change diagram logic?

No. Mermaid themes only affect visual style, not the structure or logic of your diagram.

Which Mermaid theme is best for presentations?

Presentation-friendly themes like Excalidraw (hand-drawn) or higher-contrast themes are often best for slides, depending on your audience and background.