Return After Failed Login Attempt PHP

I Am Developing login Form In PHp
The Form Is As Follows

<form method="post" action="Login.php" id="Log">
 <select id="Login" name="Type">
 <option value="Sel" selected="selected">Select Login type</option>
 <option value="Student">Student</option>
 <option value="Faculity">Faculity</option>
 </select>
 <div id="type">
 <p id="Ch">Group Id: &nbsp;<input id="l" name="log" type="text"/></p>
 <p id="Pass">Password: &nbsp; <input id="p" name="Pass" type="password" /></p>
 <input id="Cond" type="Text" />
 <input type="submit" value="Login"  />
 <p id="Invalid" style="padding-top:.75em; color:#FF0000;">Invalid Login Or Password</p>
 </form>
 

In Post.php I Connect With Database And Check Login And Passwords
I Want To Show The Tag When Password Or Login don't Match In The Same Form Below It Without Any Delay
The Is Hidden At The Beginning And Only Be Shown When Login Or Pasword Is Incorrect
How Can I Achieve This Kindly Tell me I Connect With Database Through PHP

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