refrain from fancy GUI style (in contrast to 904b2144e9c5), which looks bad in Isabelle/VSCode;

--- a/src/Pure/GUI/gui.scala	Sat Feb 15 15:06:38 2025 +0100
+++ b/src/Pure/GUI/gui.scala	Sat Feb 15 16:12:29 2025 +0100
@@ -147,7 +147,7 @@
       val b = name.nonEmpty
       style.make_text(prefix) +
         if_proper(a || b,
-          if_proper(prefix, ": ") + if_proper(kind, style.make_bold(kind)) +
+          if_proper(prefix, ": ") + if_proper(kind, style.make_text(kind)) +
           if_proper(a && b, " ") + if_proper(b, style.make_text(quote(name))))
     }
   }