$myusername = mysqli_real_escape_string($db,$_POST['username']);
  $mypassword = mysqli_real_escape_string($db,$_POST['password']);

  $sql = "SELECT id FROM admin WHERE username = '$myusername' and passcode = '$mypassword'";
  $result = mysqli_query($db,$sql);
  $row = mysqli_fetch_array($result,MYSQLI_ASSOC);
  $active = $row['active'];

  $count = mysqli_num_rows($result);

 // If result matched $myusername and $mypassword, table row must be 1 row

 if($count == 1) {
    session_register("myusername");
    $_SESSION['login_user'] = $myusername;

    header("location: welcome.php");
 }else {
    $error = "Your Login Name or Password is invalid";
 }

<style type = "text/css">
    body {
       font-family:Arial, Helvetica, sans-serif;
       font-size:14px;
    }
    label {
       font-weight:bold;
       width:100px;
       font-size:14px;
    }
    .box {
       border:#666666 solid 1px;
    }
 </style>

<div align = "center">
    <div style = "width:300px; border: solid 1px #333333; " align = "left">
       <div style = "background-color:#333333; color:#FFFFFF; padding:3px;"><b>Login</b></div>

       <div style = "margin:30px">

          <form action = "" method = "post">
             <label>UserName  :</label><input type = "text" name = "username" class = "box"/><br /><br />
             <label>Password  :</label><input type = "password" name = "password" class = "box" /><br/><br />
             <input type = "submit" value = " Submit "/><br />
          </form>

          <div style = "font-size:11px; color:#cc0000; margin-top:10px"><?php echo $error; ?></div>

       </div>

    </div>

 </div>