How to add seperator/border between content's on a post

quick and dirty way is to add <hr> tag after your post content in your posts editor using text mode

your mean by style.css / Editor

No, I believe he means the post text editor. When you create/edit a post, switch from Visual to Text mode and insert the <hr> tag after the body text of your post. You can see how it works here.

no i want to edit on content not on post

Then it sounds like you’ll need a CSS solution. Unfortunately we can’t help with those unless you present a webpage that you want to style.

See this one for better understanding- https://hackedia.net/disk-storage-analyzer-pro-v3-0-1-8-cracked-apk-is-here-latest/
i want insert a border/seperator after text mean on that- https://s2.postimg.org/pssiz6c8p/efv.png