Your question is what we call a cookie-baking question: just because you type your HTML with Notepad++ doesn’t mean that a Notepad++ is the appropriate place to ask your HTML question. (See our FAQ: https://community.notepad-plus-plus.org/topic/15958/faq-desk-you-ve-asked-your-question-in-the-wrong-place . The easy way to tell if your question belongs here is if you would expect the same answer whether you use Notepad++ or notepad.exe or SomeRandomEditor to edit your code: if the answer would be the same, then this isn’t the right forum.)
However, your HTML problem is pretty easy to spot: <h1 najlepsze filmy is not valid HTML: you probably meant something like <h1>najlepsze filmy </h1>. Since there is no closing >, the <h1> tag is never finished, so your browser has nothing to render.
Further, though it’s unrelated to your problem, the way to close the body element is </body>, not the <body/> that you use.
If you have further HTML questions, please find an HTML-focused forum.