Variable: custom-safe-themes

Themes that are considered safe to load.
If the value is a list, each element should be either the SHA-256
hash of a safe theme file, or the symbol `default', which stands
for any theme in the built-in Emacs theme directory (a directory
named "themes" in `data-directory').

If the value is t, Emacs treats all themes as safe.

This variable cannot be set in a Custom theme.