Hi Tegger,
Let me explain a bit here.
On the page: https://e-tablo.eu/sztorik-tortenetek , this is a page from T4 Builder, typography for this page will inherit the settings in T4 Builder.
But when you click to open an article, that single article page is not T4 Builder page and it will inherit the typo from template - T4 Blank and you should configure in Backend >> Extensions >> Templates >> T4 Blank template.
The style of T4 Builder will be applied for T4 Builder pages only.
Regards