performance – Some files result in ‘403 forbidden’ even with correct permissions

I have a sudden error in which css and other files are not loaded into the website. Server responds with a 403 forbidden error when I try to access them. I have given read permissions to apache for all files and folders . However, selective css style files and other files are not accessible in the website.

Does anyone have any suggestions? It would be a big help. Thank you!

I am using Drupal 7