Zhiyi Zhang (@zhiyi) commented about programs/winecfg/theme.c:
/* UXTHEME functions not in the headers */
+typedef struct
You can move the AppTheme definition into init_dialog as well. For example:
static const struct { DWORD value; const WCHAR *desc; } app_themes[] = { {1, L"Light"}, {0, L"Dark"}, };