The other answers are correct, in the chmod -R 755 will set the permissions to all the files and subfolders in a tree. It might make sense for these directories, but why set a execute bit on all files?
I suspect what you want to do is set some directories to 755 and either leave these files alone or set them to 644. For this, you can use this find command. For example:
To change all these directories to 755 (drwxr-xr-x):
find /opt/lampp/htdocs -type d -exec chmod 755 {} \;
To change all these files to 644 (-rw-r--r--):
find /opt/lampp/htdocs -type f -exec chmod 644 {} \;
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