Do you create a page in the admin area or custom PHP page?
Core Page - you need to add css via theme with e107::css
Custom PHP page - before loading header part with e107::css
this code: <link href='tabsy.css' rel='stylesheet' type='text/css'> is not allowed inside editable area (TinyMCE strips this)
Everything depends on your theme. The bootstrap theme has tabs by default.
There is a plugin for inserting head css part directly via the admin area if you are not familiar with e107::css, you can use this one. Insert header and footer