amp-reader-mode-comments.php

<?php
/**
 * AMP Reader Mode Comments plugin initialization file.
 *
 * @package   AMP_Reader_Mode_Comments
 * @author    Weston Ruter, Google
 * @link      https://gist.github.com/westonruter/b14c95d5e8531dbc1167ebfc80c74562
 * @license   GPL-2.0-or-later
 * @copyright 2019 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: AMP Reader Mode Comments
 * Plugin URI: https://gist.github.com/westonruter/b14c95d5e8531dbc1167ebfc80c74562
 * Description: Demonstration of adding comments to Reader mode templates. This requires AMP plugin v1.5 or greater.
 * Version: 0.1
 * Author: Weston Ruter, Google
 * Author URI: https://weston.ruter.net/
 * License: GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * Gist Plugin URI: https://gist.github.com/westonruter/b14c95d5e8531dbc1167ebfc80c74562
 */

add_filter(
	'amp_post_template_file',
	function ( $file, $template_type ) {

		// Abort if AMP plugin is older than v1.5.
		if ( ! defined( 'AMP__VERSION' ) || version_compare( AMP__VERSION, '1.5', '<' ) ) {
			return $file;
		}

		// Replace a comments link with the comments list and comments form.
		if ( 'meta-comments-link' === $template_type ) {
			$file = __DIR__ . '/comments.php';
		}

		return $file;
	},
	10,
	2
);

comments.php

<?php

wp_register_style( 'amp-reader-mode-comments', plugin_dir_url( __FILE__ ) . 'style.css', [], '0.1' );
wp_print_styles( [ 'amp-reader-mode-comments' ] );

comments_template();

style.css

/* CSS here is copied from Twenty Eleven */
/* @todo The CSS is not complete. It needs to be fleshed out. */

/* =Comments
----------------------------------------------- */

#comments-title {
	color: #666;
	font-size: 10px;
	font-weight: 500;
	line-height: 2.6em;
	padding: 0 0 2.6em;
	text-transform: uppercase;
}
.nopassword,
.nocomments {
	color: #aaa;
	font-size: 24px;
	font-weight: 100;
	margin: 26px 0;
	text-align: center;
}
.commentlist {
	list-style: none;
	margin: 0 auto;
	width: 68.9%;
}
.content .commentlist,
.page-template-sidebar-page-php .commentlist {
	width: 100%; /* reset the width for the one-column and sidebar page layout */
}
.commentlist > li.comment {
	background: #f6f6f6;
	border: 1px solid #ddd;
	-moz-border-radius: 3px;
	border-radius: 3px;
	margin: 0 0 1.625em;
	padding: 1.625em;
	position: relative;
}
.commentlist .pingback {
	margin: 0 0 1.625em;
	padding: 0 1.625em;
}
.commentlist .children {
	list-style: none;
	margin: 0;
}
.commentlist .children li.comment {
	background: #fff;
	border-left: 1px solid #ddd;
	-moz-border-radius: 0 3px 3px 0;
	border-radius: 0 3px 3px 0;
	margin: 1.625em 0 0;
	padding: 1.625em;
	position: relative;
}
.commentlist .children li.comment .fn {
	display: block;
}
.comment-meta .fn {
	font-style: normal;
}
.comment-meta {
	color: #666;
	font-size: 12px;
	line-height: 2.2em;
}
.commentlist .children li.comment .comment-meta {
	line-height: 1.625em;
	margin-left: 50px;
}
.commentlist .children li.comment .comment-content {
	margin: 1.625em 0 0;
	word-wrap: break-word;
	-webkit-hyphens: auto;
	-moz-hyphens: auto;
	hyphens: auto;
}
.comment-meta a {
	font-weight: bold;
}
.comment-meta a:focus,
.comment-meta a:active,
.comment-meta a:hover {
}
.commentlist .avatar {
	-moz-border-radius: 3px;
	border-radius: 3px;
	-webkit-box-shadow: 0 1px 2px #ccc;
	-moz-box-shadow: 0 1px 2px #ccc;
	box-shadow: 0 1px 2px #ccc;
	left: -102px;
	padding: 0;
	position: absolute;
	top: 0;
}
.commentlist > li:before {
	content: url(images/comment-arrow.png);
	left: -21px;
	position: absolute;
}
.commentlist > li.pingback:before {
	content: '';
}
.commentlist .children .avatar {
	background: none;
	-webkit-box-shadow: none;
	-moz-box-shadow: none;
	box-shadow: none;
	left: 2.2em;
	padding: 0;
	top: 2.2em;
}
a.comment-reply-link {
	background: #eee;
	-moz-border-radius: 3px;
	border-radius: 3px;
	color: #666;
	display: inline-block;
	font-size: 12px;
	padding: 0 8px;
	text-decoration: none;
}
a.comment-reply-link:hover,
a.comment-reply-link:focus,
a.comment-reply-link:active {
	background: #888;
	color: #fff;
}
a.comment-reply-link > span {
	display: inline-block;
	position: relative;
	top: -1px;
}

/* Post author highlighting */
.commentlist > li.bypostauthor {
	background: #ddd;
	border-color: #d3d3d3;
}
.commentlist > li.bypostauthor .comment-meta {
	color: #575757;
}
.commentlist > li.bypostauthor .comment-meta a:focus,
.commentlist > li.bypostauthor .comment-meta a:active,
.commentlist > li.bypostauthor .comment-meta a:hover {
}
.commentlist > li.bypostauthor:before {
	content: url(images/comment-arrow-bypostauthor.png);
}

/* Post Author threaded comments */
.commentlist .children > li.bypostauthor {
	background: #ddd;
	border-color: #d3d3d3;
}

/* Comment Form */
#respond {
	background: #ddd;
	border: 1px solid #d3d3d3;
	-moz-border-radius: 3px;
	border-radius: 3px;
	margin: 0 auto 1.625em;
	padding: 1.625em;
	position: relative;
	width: 68.9%;
}
#respond input[type="text"],
#respond textarea {
	background: #fff;
	border: 4px solid #eee;
	-moz-border-radius: 5px;
	border-radius: 5px;
	-webkit-box-shadow: inset 0 1px 3px rgba(204,204,204,0.95);
	-moz-box-shadow: inset 0 1px 3px rgba(204,204,204,0.95);
	box-shadow: inset 0 1px 3px rgba(204,204,204,0.95);
	position: relative;
	padding: 10px;
	text-indent: 80px;
}
#respond .comment-form-author,
#respond .comment-form-email,
#respond .comment-form-url,
#respond .comment-form-comment {
	position: relative;
}
#respond .comment-form-author label,
#respond .comment-form-email label,
#respond .comment-form-url label,
#respond .comment-form-comment label {
	background: #eee;
	-webkit-box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
	-moz-box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
	box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
	color: #555;
	display: inline-block;
	font-size: 13px;
	left: 4px;
	min-width: 60px;
	padding: 4px 10px;
	position: relative;
	top: 40px;
	z-index: 1;
}
#respond input[type="text"]:focus,
#respond textarea:focus {
	text-indent: 0;
	z-index: 1;
}
#respond textarea {
	resize: vertical;
	width: 95%;
}
#respond .comment-form-author .required,
#respond .comment-form-email .required {
	color: #bd3500;
	font-size: 22px;
	font-weight: bold;
	left: 75%;
	position: absolute;
	z-index: 1;
}
#respond .comment-notes,
#respond .logged-in-as {
	font-size: 13px;
}
#respond p {
	margin: 10px 0;
}
#respond .form-submit {
	float: right;
	margin: -20px 0 10px;
}
#respond input#submit {
	background: #222;
	border: none;
	-moz-border-radius: 3px;
	border-radius: 3px;
	-webkit-box-shadow: 0px 1px 2px rgba(0,0,0,0.3);
	-moz-box-shadow: 0px 1px 2px rgba(0,0,0,0.3);
	box-shadow: 0px 1px 2px rgba(0,0,0,0.3);
	color: #eee;
	cursor: pointer;
	font-size: 15px;
	margin: 20px 0;
	padding: 5px 42px 5px 22px;
	position: relative;
	left: 30px;
	text-shadow: 0 -1px 0 rgba(0,0,0,0.3);
}
#respond input#submit:active {
	background: #1982d1;
	color: #bfddf3;
}
#respond #cancel-comment-reply-link {
	color: #666;
	margin-left: 10px;
	text-decoration: none;
}
#respond .logged-in-as a:hover,
#respond #cancel-comment-reply-link:hover {
	text-decoration: underline;
}
.commentlist #respond {
	margin: 1.625em 0 0;
	width: auto;
}
#reply-title {
	color: #373737;
	font-size: 24px;
	font-weight: bold;
	line-height: 30px;
}
#cancel-comment-reply-link {
	color: #888;
	display: block;
	font-size: 10px;
	font-weight: normal;
	line-height: 2.2em;
	letter-spacing: 0.05em;
	position: absolute;
	right: 1.625em;
	text-decoration: none;
	text-transform: uppercase;
	top: 1.1em;
}
#cancel-comment-reply-link:focus,
#cancel-comment-reply-link:active,
#cancel-comment-reply-link:hover {
	color: #ff4b33;
}
#respond label {
	line-height: 2.2em;
}
#respond input[type=text] {
	display: block;
	height: 24px;
	width: 75%;
}
#respond p {
	font-size: 12px;
}
#respond #wp-comment-cookies-consent {
	margin: 0 10px 0 0;
}
p.comment-form-comment {
	margin: 0;
}
.form-allowed-tags {
	display: none;
}

Installation instructions: https://gist.github.com/westonruter/6110fbc4bef0c4b8c021a112012f7e9c