When I use the svg output format, horizontal lines in class definition seems to short. I tried with several different svg tools (Ilustrator, Inkscape, Firefox) to check the output.
Below is a minimal example:
@startuml
skinparam backgroundcolor transparent
skinparam classAttributeIconSize 0
skinparam classBorderThickness .8
hide circle
class Foo {
-name : String
}
@enduml