Error(s):

1618388902/source.cpp:12:20: error: template-id ‘biggest<>’ for ‘double biggest(box, box)’ does not match any template declaration
 template <> double biggest(const box a,const box b);
                    ^~~~~~~
1618388902/source.cpp:11:25: note: candidate is: template<class T> T biggest(T, T)
 template <typename T> T biggest(const T a,const T b);
                         ^~~~~~~
1618388902/source.cpp: In function ‘int main(int, const char**)’:
1618388902/source.cpp:16:6: warning: unused variable ‘a’ [-Wunused-variable]
  box a {"HELLO MOTHERFUCKER!!!", 0, 0, 0, 4.4};
      ^
1618388902/source.cpp:17:6: warning: unused variable ‘b’ [-Wunused-variable]
  box b {"HELLO !!!", 0, 0, 0, 4.5};
      ^
1618388902/source.cpp: At global scope:
1618388902/source.cpp:31:20: error: template-id ‘biggest<>’ for ‘double biggest(box, box)’ does not match any template declaration
 template <> double biggest(const box a,const box b)
                    ^~~~~~~
1618388902/source.cpp:22:25: note: candidate is: template<class T> T biggest(T, T)
 template <typename T> T biggest(const T a,const T b)
                         ^~~~~~~