adding additional class to get the post thumbnail [duplicate]

Sorry for late reply, already fixed, i miss understood about array, so here the code that completely run as i want it.

 <?php
 $next_post = get_next_post();
  next_post_link('%link',
     get_the_post_thumbnail($next_post->ID, 'prev_next_img', array(
               'class' => 'rounded-lg object-fill w-full max-h-full' 
     )) . '<h4 class="text-center mt-2 lg:text-base text-sm no-underline text-black leading-snug font-medium">%title</h4>',                                                
     false);
 ?>

in function.php

i put custome image size

add_image_size('prev_next_img', 370, 270, true);