Advanced Mermaid Features

Advanced configuration, styling, theming, and other powerful features for creating professional diagrams.

Frontmatter Configuration

Add YAML configuration at the top of diagrams:

---
config:
  theme: dark
  themeVariables:
    primaryColor: "#ff6b6b"
    primaryTextColor: "#fff"
    primaryBorderColor: "#333"
    lineColor: "#666"
    secondaryColor: "#4ecdc4"
    tertiaryColor: "#ffe66d"
---
flowchart TD
    A --> B

Themes

Built-in Themes

---
config:
  theme: default
---

Available themes:

• default - Standard blue theme
• forest - Green earth tones
• dark - Dark mode friendly
• neutral - Grayscale professional
• base - Minimal base theme for customization

Theme Examples

Default Theme:

---
config:
  theme: default
---
flowchart LR
    A[Start] --> B[Process]
    B --> C{Decision}
    C -->|Yes| D[Action 1]
    C -->|No| E[Action 2]

Dark Theme:

---
config:
  theme: dark
---
flowchart LR
    A[Start] --> B[Process]
    B --> C{Decision}

Forest Theme:

---
config:
  theme: forest
---
flowchart LR
    A[Start] --> B[Process]

Custom Theme Variables

Override specific colors:

---
config:
  theme: base
  themeVariables:
    primaryColor: "#ff6b6b"
    primaryTextColor: "#fff"
    primaryBorderColor: "#d63031"
    lineColor: "#74b9ff"
    secondaryColor: "#00b894"
    tertiaryColor: "#fdcb6e"
    background: "#f0f0f0"
    mainBkg: "#ffffff"
    textColor: "#333333"
    nodeBorder: "#333333"
    clusterBkg: "#f9f9f9"
    clusterBorder: "#666666"
---
flowchart TD
    A --> B --> C

Layout Options

Dagre Layout (Default)

---
config:
  layout: dagre
---
flowchart TD
    A --> B

ELK Layout (Advanced)

For complex diagrams with better automatic layout:

---
config:
  layout: elk
  elk:
    mergeEdges: true
    nodePlacementStrategy: BRANDES_KOEPF
---
flowchart TD
    A --> B

ELK node placement strategies:

• SIMPLE - Basic placement
• NETWORK_SIMPLEX - Network optimization
• LINEAR_SEGMENTS - Linear arrangement
• BRANDES_KOEPF - Balanced (default)

Look Options

Classic Look

Traditional Mermaid appearance:

---
config:
  look: classic
---
flowchart LR
    A --> B --> C

Hand-Drawn Look

Sketch-like, informal style:

---
config:
  look: handDrawn
---
flowchart LR
    A --> B --> C

Complete Configuration Example

---
config:
  theme: base
  look: handDrawn
  layout: dagre
  themeVariables:
    primaryColor: "#ff6b6b"
    primaryTextColor: "#fff"
    primaryBorderColor: "#d63031"
    lineColor: "#74b9ff"
    secondaryColor: "#00b894"
    tertiaryColor: "#fdcb6e"
---
flowchart TD
    Start([Begin Process]) --> Input[Gather Data]
    Input --> Process{Valid?}
    Process -->|Yes| Store[(Save to DB)]
    Process -->|No| Error[Show Error]
    Store --> Notify[Send Notification]
    Error --> Input
    Notify --> End([Complete])

Diagram-Specific Styling

Flowchart Styling

Class-based styling:

flowchart TD
    A[Normal]:::success
    B[Warning]:::warning
    C[Error]:::error
    
    classDef success fill:#00b894,stroke:#00a383,color:#fff
    classDef warning fill:#fdcb6e,stroke:#e8b923,color:#333
    classDef error fill:#ff6b6b,stroke:#ee5253,color:#fff
    
    A --> B --> C

Node-specific styling:

flowchart LR
    A[Node A]
    B[Node B]
    C[Node C]
    
    style A fill:#ff6b6b,stroke:#333,stroke-width:4px
    style B fill:#4ecdc4,stroke:#333,stroke-width:2px
    style C fill:#ffe66d,stroke:#333,stroke-width:2px
    
    A --> B --> C

Link styling:

flowchart LR
    A --> B
    B --> C
    C --> D
    
    linkStyle 0 stroke:#ff6b6b,stroke-width:4px
    linkStyle 1 stroke:#4ecdc4,stroke-width:2px
    linkStyle 2 stroke:#ffe66d,stroke-width:2px

Sequence Diagram Styling

sequenceDiagram
    participant A
    participant B
    participant C
    
    A->>B: Message 1
    B->>C: Message 2
    
    Note over A,C: Styled note
    
    %%{init: {'theme':'forest'}}%%

Class Diagram Styling

classDiagram
    class User {
        +String name
        +login()
    }
    
    class Admin {
        +manageUsers()
    }
    
    User <|-- Admin
    
    %%{init: {'theme':'dark'}}%%

Directional Hints

Control layout direction for specific nodes:

flowchart TB
    A --> B
    B --> C
    B --> D
    C --> E
    D --> E
    
    %% This is a comment - helps organize complex diagrams

Click Events and Links

Add interactive elements:

flowchart LR
    A[GitHub]
    B[Documentation]
    C[Live Demo]
    
    click A "https://github.com" "Go to GitHub"
    click B "https://mermaid.js.org" "View Docs"
    click C "https://mermaid.live" "Try Live Editor"
    
    A --> B --> C

Tooltips

Add hover information:

flowchart LR
    A[Service A]
    B[Service B]
    
    A -.->|REST API| B
    
    %% Tooltips are defined with links
    link A: API Documentation @ https://api.example.com
    link B: Service Dashboard @ https://dashboard.example.com

Subgraph Styling

flowchart TB
    subgraph Frontend
        A[Web App]
        B[Mobile App]
    end
    
    subgraph Backend
        C[API]
        D[Database]
    end
    
    A & B --> C
    C --> D
    
    style Frontend fill:#e3f2fd,stroke:#2196f3,stroke-width:2px
    style Backend fill:#fff3e0,stroke:#ff9800,stroke-width:2px

Comments and Documentation

flowchart TD
    %% This is a single-line comment
    
    %% Multi-line comments can be created
    %% by using multiple comment lines
    
    A[Start]
    B[Process]
    C[End]
    
    %% Define relationships
    A --> B
    B --> C
    
    %% Add styling
    style A fill:#90EE90
    style C fill:#FFB6C1

Complex Styling Example

flowchart TB
    subgraph production[Production Environment]
        direction LR
        lb[Load Balancer]
        
        subgraph servers[Application Servers]
            app1[Server 1]
            app2[Server 2]
            app3[Server 3]
        end
        
        cache[(Redis Cache)]
        db[(PostgreSQL)]
    end
    
    subgraph monitoring[Monitoring]
        logs[Log Aggregator]
        metrics[Metrics Dashboard]
    end
    
    users[Users] --> lb
    lb --> app1 & app2 & app3
    app1 & app2 & app3 --> cache
    app1 & app2 & app3 --> db
    app1 & app2 & app3 --> logs
    logs --> metrics
    
    style production fill:#e8f5e9,stroke:#4caf50,stroke-width:3px
    style servers fill:#fff3e0,stroke:#ff9800,stroke-width:2px
    style monitoring fill:#e3f2fd,stroke:#2196f3,stroke-width:2px
    
    style lb fill:#ffeb3b,stroke:#fbc02d,stroke-width:2px
    style cache fill:#ce93d8,stroke:#ab47bc,stroke-width:2px
    style db fill:#ce93d8,stroke:#ab47bc,stroke-width:2px
    
    classDef serverClass fill:#81c784,stroke:#4caf50,stroke-width:2px,color:#000
    class app1,app2,app3 serverClass
    
    linkStyle 0,1,2,3 stroke:#4caf50,stroke-width:2px
    linkStyle 4,5,6,7,8,9 stroke:#ff9800,stroke-width:1px

Responsive Sizing

Use CSS to make diagrams responsive:

<div style="max-width: 100%; overflow: auto;">
    <pre class="mermaid">
        flowchart LR
            A --> B --> C
    </pre>
</div>

SVG Export Options

When exporting to SVG:

# Export with custom dimensions
mmdc -i diagram.mmd -o output.svg -w 1920 -H 1080

# Export with background color
mmdc -i diagram.mmd -o output.svg -b "#ffffff"

# Export with transparent background
mmdc -i diagram.mmd -o output.svg -b "transparent"

Best Practices for Advanced Features

1. Use themes consistently - Pick one theme for related diagrams
2. Don't over-style - Too many colors can reduce clarity
3. Test hand-drawn look - Some diagrams work better with classic look
4. Use ELK for complex layouts - When dagre creates crossed lines
5. Comment complex configurations - Explain non-obvious styling choices
6. Keep it accessible - Ensure sufficient color contrast
7. Test exports - Verify diagrams render correctly in target format
8. Version control configs - Track theme changes in your repository

Accessibility Considerations

---
config:
  theme: base
  themeVariables:
    primaryColor: "#0066cc"
    primaryTextColor: "#ffffff"
    primaryBorderColor: "#003d7a"
    lineColor: "#333333"
    background: "#ffffff"
    mainBkg: "#f0f0f0"
---
flowchart TD
    A[High Contrast Text] --> B[Clear Labels]
    B --> C[Meaningful Colors]

Accessibility tips:

• Use high contrast color combinations
• Don't rely solely on color to convey meaning
• Include descriptive text labels
• Test with color blindness simulators
• Consider dark mode alternatives

Performance Considerations

For large diagrams:

---
config:
  layout: elk
  elk:
    mergeEdges: true
---
flowchart TD
    %% ELK handles complex layouts better
    %% Merge edges reduces visual clutter

Performance tips:

• Use ELK layout for diagrams with >20 nodes
• Enable edge merging for simplified connections
• Split very large diagrams into multiple focused views
• Consider using subgraphs to organize complexity
• Limit styling to essential elements

Integration Examples

Markdown Files

# System Architecture

```mermaid
flowchart LR
    A --> B
```

HTML Files

<!DOCTYPE html>
<html>
<head>
    <script type="module">
        import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
        mermaid.initialize({ 
            startOnLoad: true,
            theme: 'dark',
            look: 'handDrawn'
        });
    </script>
</head>
<body>
    <pre class="mermaid">
        flowchart LR
            A --> B
    </pre>
</body>
</html>

React Components

import React from 'react';
import mermaid from 'mermaid';

mermaid.initialize({
    startOnLoad: true,
    theme: 'forest'
});

function DiagramComponent() {
    React.useEffect(() => {
        mermaid.contentLoaded();
    }, []);
    
    return (
        <div className="mermaid">
            flowchart LR
                A --> B
        </div>
    );
}