beta-style: Manage padding in sequence diagram

Question

Hi PlantUML

Could you please explain how to manage 'padding' style for sequence diagram

In the below example, font attributes seems to work well but padding does not take effect.

@startuml

<style>

root {

    Padding 100

}

Participant {

Padding 100

FontColor Red

FontSize 10

}

.mystyle

{

FontColor Blue

FontStyle Italic

}

</style>

Participant A

Participant B<<mystyle>>

Participant C

A->B: Test message

@enduml

http://www.plantuml.com/plantuml/png/LOzD2i8m58JNUQTu5r3hLaBe3mZkYdg1q3nA84saIHUrU7TVf4ARh8QPRoOfOz9ZcWO7CgRPaG8nXf1m0UGZMcsCzJsUYm91V0JmRHcmdNrfdsDYcs5r3JurmOKHxsHM_R1lOfiBCdySvjyKY6MNhzr4Vo3xU4lQsIvJyhG-3hRZrKxLKgx5IksC1g0wgFg2Jue91ufHzmGbUSFV_W80

Thanks

B