Add custom button classes to Event Espresso 4 submit form inputs

my_uikit_add_button_classes.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_action('template_redirect', 'my_change_venue_details');
function my_change_venue_details() {
  global $post;
  if(!class_exists('EE_Registry')) {
    return;
  }
  if (
    $post instanceof WP_Post 
    && $post->post_type == 'espresso_events'
    || is_page(EE_Registry::instance()->CFG->core->reg_page_id)
  ) {
    add_filter('the_content', 'my_uikit_add_button_classes', 999, 1);
  }
}

function my_uikit_add_button_classes($content) {
  $patterns = array();
  $patterns[0] = 'class="spco-next-step-btn';
  $patterns[1] = 'ticket-selector-submit-ajax';
  $patterns[2] = 'view-details-btn';
  $replacements = array();
  $replacements[0] = 'class="spco-next-step-btn uk-button uk-button-primary';
  $replacements[1] = 'ticket-selector-submit-ajax uk-button uk-button-primary';
  $replacements[2] = 'view-details-btn uk-button uk-button-primary"';
  $content = str_replace($patterns, $replacements, $content);
  return $content;
}