Compiled but with warnings

Hello all,
My reactjs website can run but is compiled with warnings. I ignore the warnings or how can I fix the warnings?
1st.js
'React' is defined but never used no-unused-vars

2nd.js
Duplicate key 'background' no-dupe-keys

3rd.js
Duplicate key 'background' no-dupe-keys

Search for the keywords to learn more about each warning.
To ignore, add // eslint-disable-next-line to the line before. Thanks!