SDL_SystemTheme.3type - Man Page

#include <SDL3/SDL_video.h>

typedef enum SDL_SystemTheme
{
    SDL_SYSTEM_THEME_UNKNOWN,   /**< Unknown system theme */
    SDL_SYSTEM_THEME_LIGHT,     /**< Light colored system theme */
    SDL_SYSTEM_THEME_DARK       /**< Dark colored system theme */
} SDL_SystemTheme;

This enum is available since SDL 3.2.0.