Back to top WordPress AMP plugin

backtotop.css

html {
	scroll-behavior: smooth;
  }
  body {
	position: relative;
  }
  
  .scrolltop-wrap {
	box-sizing: border-box;
	position: absolute;
	top: 12rem;
	right: 2rem;
	bottom: 0;
	pointer-events: none;
	-webkit-backface-visibility: hidden;
			backface-visibility: hidden;
  } 
  
  
  
  @supports (-moz-appearance: meterbar) {
	.scrolltop-wrap {
	  clip: rect(0, 3rem, auto, 0);
	}
  }
  .scrolltop-wrap a {
	position: fixed;
	position: -webkit-sticky;
	position: sticky;
	top: -5rem;
	width: 3rem;
	height: 3rem;
	margin-bottom: -5rem;
	-webkit-transform: translateY(100vh);
			transform: translateY(100vh);
	-webkit-backface-visibility: hidden;
			backface-visibility: hidden;
	display: inline-block;
	text-decoration: none;
	-webkit-user-select: none;
	   -moz-user-select: none;
		-ms-user-select: none;
			user-select: none;
	pointer-events: all;
	outline: none;
	overflow: hidden;
  }
  .scrolltop-wrap a svg {
	display: block;
 
	width: 100%;
	height: 100%;
  }
  .scrolltop-wrap a svg path {
	-webkit-transition: all 0.1s;
	transition: all 0.1s;
  }
  .scrolltop-wrap a #scrolltop-arrow {
	-webkit-transform: scale(0.66);
			transform: scale(0.66);
	-webkit-transform-origin: center;
			transform-origin: center;
  }
  @media print {
	.scrolltop-wrap {
	  display: none !important;
	}
  }
  
  html {
	overflow-y: scroll;
	overflow-x: hidden;
  }  


  .scrolltop-wrap a svg path{
    fill: #21759b  ;
}

backtotop.php

<?php
/**
 * Plugin Name: Back to Top & AMP - jamesozz.ie
 * Plugin URI: http://www.jamesozz.ie
 * Description: Back to top button. JavaScript free & AMP compatible
 * Version: 1.0
 * Author: James Osborne
 * Author URI: http://www.jamesozz.ie
 */

add_action('wp_footer', function(){  
     echo '
     

<div class="scrolltop-wrap">
<a href="#" role="button" aria-label="Scroll to top">
<svg viewBox="0 0 612 612" style="enable-background:new 0 0 612 612;"  > 
    
<path d="M256,0C114.833,0,0,114.833,0,256s114.833,256,256,256s256-114.833,256-256S397.167,0,256,0z M383.188,302.75
			c-1.646,3.979-5.542,6.583-9.854,6.583h-32c-2.833,0-5.542-1.125-7.542-3.125L256,228.417l-77.792,77.792
			c-2,2-4.708,3.125-7.542,3.125h-32c-4.313,0-8.208-2.604-9.854-6.583c-1.604-3.979-0.729-8.583,2.313-11.625l117.333-117.333
			c4.167-4.167,10.917-4.167,15.083,0l117.333,117.333c2.042,2.042,3.125,4.771,3.125,7.542
			C384,300.042,383.729,301.438,383.188,302.75z"/>


 
</svg>
</a>
</div>

    
    '
    ; });


function wpse_load_plugin_css() {
    $plugin_url = plugin_dir_url( __FILE__ );
    wp_enqueue_style( 'style1', $plugin_url . 'backtotop.css' );
}
add_action( 'wp_enqueue_scripts', 'wpse_load_plugin_css' );