Can't build master on linux: FileHelper.h:8:62: error: ‘size_t’ has not been declared

hello, When I tried to compile https://github.com/pcwalton/gltf-ibl-sampler-egui , it kept failing on FileHelper.h:8:62: error: ‘size_t’ has not been declared. All I did is clone that repo, then this one as submodule. I'm not knowledgeable about cpp, so this is all I can provide. Probably I'm doing something wrong, would be nice to know what.

djkato@djkato-vfx ~/C/g/glTF-IBL-Sampler (master)> cmake .
-- The C compiler identification is GNU 11.4.1
-- The CXX compiler identification is GNU 11.4.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- 'IBLSAMPLER_EXPORT_SHADERS' is FALSE
volk: using VULKAN_HEADERS_INSTALL_DIR option
-- 
-- Configuring done (0.2s)
-- Generating done (0.0s)
-- Build files have been written to: /home/djkato/Code/gltf-ibl-sampler-egui/glTF-IBL-Sampler

djkato@djkato-vfx ~/C/g/glTF-IBL-Sampler (master)> make
[  9%] Building C object thirdparty/volk/CMakeFiles/volk.dir/volk.c.o
[ 18%] Linking C static library libvolk.a
[ 18%] Built target volk
[ 27%] Building CXX object CMakeFiles/GltfIblSampler.dir/lib/source/FileHelper.cpp.o
In file included from /home/djkato/Code/gltf-ibl-sampler-egui/glTF-IBL-Sampler/lib/source/FileHelper.cpp:1:
/home/djkato/Code/gltf-ibl-sampler-egui/glTF-IBL-Sampler/lib/source/FileHelper.h:8:62: error: ‘size_t’ has not been declared
    8 |         bool writeFile(const char* _path, const char* _data, size_t _bytes);
      |                                                              ^~~~~~
/home/djkato/Code/gltf-ibl-sampler-egui/glTF-IBL-Sampler/lib/source/FileHelper.cpp:28:75: error: ‘bool IBLLib::writeFile(const char*, const char*, size_t)’ should have been declared inside ‘IBLLib’
   28 | bool IBLLib::writeFile(const char* _path, const char* _data, size_t _bytes)
      |                                                                           ^
make[2]: *** [CMakeFiles/GltfIblSampler.dir/build.make:76: CMakeFiles/GltfIblSampler.dir/lib/source/FileHelper.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:102: CMakeFiles/GltfIblSampler.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

KhronosGroup / glTF-IBL-Sampler

Can't build master on linux: FileHelper.h:8:62: error: ‘size_t’ has not been declared #30