A modules theme classes define the look and feel of a module.
graph TD;
  classDef default fill:#eaeaea,stroke:#666,stroke-width:2px;
  classDef active fill:#fff,stroke:#666,stroke-width:2px;
  MODULES(Modules);
  MODULE1(Module 1);
  MODULES---MODULE1;
  MODULE1---MODULES-BASE(Base);
  MODULE1---MODULES-MODIFIER(Modifier);
  MODULE1---MODULES-STATE(State);
  MODULE1---MODULES-THEME(Theme);
  MODULE1---MODULES-LAYOUT(Layout);
  class MODULES-THEME active;
How do they work?
Themes are created using only class selectors and can contain any properties needed to change the look and feel of a module.
How do I use them?
Theme classes are applied by appending .module-t-* and/or .module-child-t-* to one of a modules base classes.