How to hid the code from the blog's preview

I don't know much about how to code but i found out how to hid the code from the blog preview.

You just need to use [<!-- (code) --->] but use it after the <style> and before the </style> 

Like <style> <!-- (code) ---> </style> 

(Its really important to note that the first one has only two[--]!!!! <!--)