index.php

<?php
/**
 * Plugin Name: Social Buttons
 * Plugin URI: https://www.sebadima.com
 * Description: A simple plugin to share a post on socials networks.
 * Version: 1.3a
 * Author: Sebastiano Dimartina
 * Author URI: https://www.sebadima.com
 */

add_action( 'the_content', 'dsse_sharing' );
add_action( 'wp_enqueue_scripts', 'dsse_load_plugin_css' );


function dsse_load_plugin_css() {
    $plugin_url = plugin_dir_url( __FILE__ );
    wp_enqueue_style( 'style', $plugin_url . 'css/style.css' );
}


function dsse_sharing ( $content ) {

   $html = "Condividi se ti è piaciuto";
   $html = $html . "<br>";

   global $post;
   $url = get_permalink($post->ID);
   $url = esc_url($url);

   $html = $html . "<div class='facebook'><a target='_blank' href='http://www.facebook.com/sharer.php?u=" . $url . "'>💙 </a></div>";
   $html = $html . "<a>&nbsp;&nbsp;</a>";
   $html = $html . "<div class='twitter'><a target='_blank' href='https://twitter.com/share?url=" . $url . "'>💙</a></div>";

   $html = $html . "<br>";
   $html = $html . "<br>";

   return $content = $content . $html;
}