Hi Manikandan,
As I understand, you encounter the issue with content editor web part.
1. You can directly input your CSS code to content editor web part instead of using Content Link. Please click Edit Source > input code > OK, then test the issue again. the URL below is a picture to show how to input your CSS code.
https://onedrive.live.com/redir?resid=40B702A9FB117DD!133&authkey=!AHkXW92RYtXZfXw&v=3&ithint=photo%2cpng
2. If you would like to link content editor web part to a file cross site collections, please use page viewer web part as workaround.
How to use page view web part:
https://support.office.com/en-gb/article/Display-a-Web-page-on-a-SharePoint-page-by-adding-the-Page-Viewer-Web-Part-7f61feec-9b3d-4805-a960-07636ba59527
Here is a similar issue for your reference:
http://sharepoint.stackexchange.com/questions/42607/how-to-resolve-cannot-retrieve-the-url-specified-in-the-content-link-property
Best regards,
Sara Fan