Describe the bug
A clear and concise description of what the bug is.
[BUG]Custom CSS shows ext.custom_css.permission_problem，can't save custom css.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Extension'
2. Click on 'Custom CSS'
3. Scroll down to the bottom
4. See error

Expected behavior
Can successfully use custom css

Screenshots
If applicable, add screenshots to help explain your problem.

Environment information (please complete the following information):

• Device:Lenovo Yoga14s[e.g. iPhone6]

• OS: windows11[e.g. Ubuntu 20.04]

• Browser:Firefox 113 [e.g. Firefox 86]

• FreshRSS version:1.20.2 [e.g. 1.17.1]

• Database version:Sqlite [e.g. Mysql 5.7]

• PHP version:7.4.33 [e.g. PHP 7.4]

• Installation type:Docker [e.g. Yunohost]

Additional context
Add any other context about the problem here.