I chose a dark theme, but when I enter a cell and begin to write codes, the color of the cell becomes bright, and it makes me feel hard to see the codes.Can I change this ?

Hi @PKUFlyingPig, looks like you're using Vim nbextension - I've had the same problem and found out in this old issue that jupyter-themes support -vim flag.
Try adding it to a command you've executed to set your current theme (as executing bare jt -vim will override the rest of your config with default jupyter theme) - you want it to look something like
jt -t oceans16 -f roboto -fs 12 -vim
judging from the screenshot you provided.
Thank you so much ! I have been suffered for the strange color for weeks. It does work for me. Thank you again!
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Thank you so much ! I have been suffered for the strange color for weeks. It does work for me. Thank you again!