How to customize theme in zoho? How to add external CSS and Javascript files. I moved my html source code in html editor but deleted my external css and javascript source code and etc. Please advice how I will achieve this.

https://support.zoho.com/portal/lingapos/home

2. I read one article about theme files structure. How to upload template files and configure please guide me.

3. Right now we are using trial back. its achievable please advice