Is there a way to apply CSS like styles to a package and class hierarchy?

Question

I would like to define some style attributes at the package level e.g. headerbackground, line thickness, show stereotype not on package but included classes. In the current documentation and some other sites i do not find any information how package and class can be adressed through hierachical styles.

Answer 1

css styling can be applied to packages

@startuml
<style>
root {
  --default-BackGroundColor: White Smoke;
  --default-DiagonalCorner: 0;
  --default-FontName: SansSerif;
  --default-FontSize: 14;
  --default-FontSize-Title: 24;
  --default-LineThickness: 2.0;
  --default-note-BackgroundColor: #white/LemonChiffon;
  --default-RoundCorner: 25;
  --default-Shadowing:3.0;
  BackGroundColor: var(--default-BackGroundColor);
  DiagonalCorner: var(--default-DiagonalCorner);
  FontColor: black;
  FontName: var(--default-FontName);
  FontSize: var(--default-FontSize);
  FontStyle: plain;
  HorizontalAlignment: left;
  HyperLinkColor: blue;
  HyperLinkUnderlineThickness: 1;
  LineColor: black;
  LineThickness: var(--default-LineThickness);
  RoundCorner: var(--default-RoundCorner);
  Shadowing: 0.0;
  }
  
  arrow {
    FontColor: black;
    FontName: Sans Serif;
    FontSize: 12;
    FontStyle: Bold;
    LineColor: black;
    LineThickness: 3;
  }
  actor {
    BackgroundColor:transparent;
    FontColor: red;
    FontSize: 12;
    FontStyle: Bold;
    LineColor: red;
    LineThickness: 3;
    RoundCorner:0;
    'RoundCorner: var(--default-RoundCorner);
    'Shadowing: 3.0;  
    Shadowing: 3.0;
  }
  package {
    BackgroundColor: #white/Aqua;
    FontColor: Blue;
    FontSize: var(--default-FontSize);
    FontStyle: Bold;
    LineColor: Blue;
    LineThickness: var(--default-LineThickness);
    RoundCorner: var(--default-RoundCorner);
    'Shadowing: 3.0;  
    Shadowing: var(--default-Shadowing);
  }    
document {
   BackgroundColor: transparent;
}
</style>
left to right direction
actor Guest as g
package Professional {
actor Chef as c
actor "Food Critic" as fc
}
package Restaurant {
usecase "Eat Food" as UC1
usecase "Pay for Food" as UC2
usecase "Drink" as UC3
usecase "Review" as UC4
}
fc --> UC4
g --> UC1
g --> UC2
g --> UC3
@enduml