As said, if you specify the "scale" directive/command the rectangle title become bold.
NOT bold:
@startuml
/' scale 250*250 '/
left to right direction
skinparam packageStyle rect
:user:
rectangle Title{
:user:--( UC1 - Login )
}
@enduml
try it (PlantUML Demo Live): https://bit.ly/2rmSFPC
bold:
@startuml
scale 250*250
left to right direction
skinparam packageStyle rect
:user:
rectangle Title{
:user:--( UC1 - Login )
}
@enduml
try it (PlantUML Demo Live): https://bit.ly/2wi3Pdb