How to use global variable in C++ module?

Question

When I use module in a C++20 project, if I have

// Camera.hpp
extern const unsigned int SCR_WIDTH;
extern const unsigned int SCR_HEIGHT;

And in main.cpp

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

But now I use module,

// Camera.cppm
module;

#include <glad/glad.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

export module Camera;

// extern const unsigned int SCR_WIDTH;
// extern const unsigned int SCR_HEIGHT;

It seems that the linker cannot find the variables, so how should I revise it?

ld.lld: error: undefined symbol: SCR_HEIGHT@Camera
>>> referenced by CMakeFiles/triangle.dir/src/triangle2.cpp.obj:(.refptr._ZW6Camera10SCR_HEIGHT)

ld.lld: error: undefined symbol: SCR_WIDTH@Camera
>>> referenced by CMakeFiles/triangle.dir/src/triangle2.cpp.obj:(.refptr._ZW6Camera9SCR_WIDTH)