first of all thanks for the answer.
as i said i tried it and although the navbar sticks to the top, the dropdown effect doesn't work anymore.
below is my code:
<!DOCTYPE html>
<html lang="en-US">
<head>
<title>Site title</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" type="text/css" href="test_style.css">
</head>
<body>
<div class="topbar">
<a href="#"><img class="logo" src="logo.png" alt="logo"></a>
<div clas