Bulma Columns and Grid interoperability for responsive layouts

Design goal is to select a Bulma layout system for a low-traffic site where CSS payload is the primary cost concern. Bulma is CSS-only with no runtime execution cost, but using the full library without a SASS build can increase payload.

The Columns system uses Flexbox with proportional width helpers and responsive modifiers such as is-mobile and is-desktop. The Grid system provides a 12-column placement model for more granular positioning. Both support responsive behavior and alignment modifiers like is-centered.

Uncertainty remains about overlap and interoperability between the two systems when used together in the same project.

Do Columns and Grid share base utilities or duplicate CSS rules? Is nesting Grid inside Columns or Columns inside Grid a supported pattern? Does combining responsive modifiers from both systems increase unused selector count in an uncompiled build?