Change CSS templates featured content slider light

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Hi
I haad download an add-on: featured content slide light and I wanted to change the font family witch is font-family: 'Yanone Kaffeesatz', arial, serif; to Calibri

So I go in my filezilla , then in /packages/c5mix_featured_content_slider/blocks/page_list/templates

Then I copy the featured_content_slide in my desktop then I copy it at the same place under the name of Myy_featured_content_slide then I open it with notepad and I change the css : just the font-family.
Then I click on upload to the new Myy_featured_content_slide and then I choose custom templates and this one on my site
But this doesn't work... It is as if no template is selected

Why?