mainpage.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" media="screen" href="main.css" />
    <script src="main.js"></script>
</head>
<body>
    <form action="server.php">
        <input type = "text" name = "mail" value="e-mail"/> <br/>
        <input type = "text" name = "ime" value="ime"/> <br/>
        <input type = "text" name = "prezime" value="prezime"/> <br/>
        <input type = "submit" value="Prijavi se"/>
    </form>
</body>
</html>