how to center my form in the middle of the page html code example

Example 1: how to get the link of the current page in php

<?php  
    if(isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on')   
         $url = "https://";   
    else  
         $url = "http://";   
    // Append the host(domain name, ip) to the URL.   
    $url.= $_SERVER['HTTP_HOST'];   
    
    // Append the requested resource location to the URL   
    $url.= $_SERVER['REQUEST_URI'];    
      
    echo $url;  
  ?>

Example 2: html align form center

form {
  text-align: center;
}

Example 3: how to align a component in the middle of page

div {
	width: 100px;
	height: 100px;
	background-color: red;
	
	position: absolute;
	top:0;
	bottom: 0;
	left: 0;
	right: 0;
  	
	margin: auto;
}