How can I style all children activities within a partition in an Activity diagram?

Question

I'd like to be able to style all the children elements/activities under a specific partition while leaving those activities outside of the partition alone. I've tried the following but it doesn't end up selecting anything and has no effect. Is there another way to accomplish this without specifically tagging each activity I want to modify?

@startuml
<style>
partition {
  activity {
    BackgroundColor: blue;
  }
}
</style>

start
partition "Partition1" {
  :Activity1;
  :Activity2;
}
:Activity3;
@enduml

Answer 1

Hi Y.,

Currently not possible, I just open this wanted feature here:

• [Style] Allow local style on Activity Diagram · Issue #2285 · plantuml/plantuml

Then here is a workaround, as you mention, by "tagging specifically each activity":

@startuml
<style>
.mystyle {
    BackgroundColor: blue;
}
</style>

start
:Activity0;
partition "Partition1" {
  :Activity1; <<mystyle>>
  :Activity2; <<mystyle>>
}

:Activity3;

@enduml

Enjoy,
Regards,
Th.

Answer 2

Hi Y.,

Here is another workaround (since v1.2025.5):

@startuml
start
:Activity0;
partition "Partition1" {
<style>
  activity {
    BackgroundColor: blue;
}
</style>
  :Activity1;
  :Activity2;
}

<style>
  activity {
    BackgroundColor: #f1f1f1;
}
</style>
:Activity3;
@enduml

See:

• [Style] Allow local style on Activity Diagram · Issue #2285 · plantuml/plantuml

Enjoy,
Regards,
Th.