#include "./raylib-4.0.0_win64_mingw-w64_ex/include/raygui.h"
...
Font font = LoadFontEx("./fonts/rainyhearts16.ttf", 12, 0, 0);
char *st_ashes = "raylib-4.0.0_win64_mingw-w64_Ex/styles/ashes/ashes.rgs";
GuiLoadStyle(st_ashes);