How can I include additional boxes or containers in a mermaid sequence diagram?

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To include additional boxes or containers in a mermaid sequence diagram, you can use the participant keyword followed by the name of the box or container that you want to add. For example:

sequenceDiagram
    participant User
    participant "Web Application"
    participant "Database Server"
    User->>"Web Application": Send data
    "Web Application"->>"Database Server": Fetch data

In this example, we have added two additional containers: "Web Application" and "Database Server". These containers are represented by rectangular boxes in the diagram. You can customize the appearance of these boxes using CSS styles or mermaid configuration options.