adding the button class to prev/next

<div class="submit">
        <input type="submit" name="profile-group-edit-submit" id="profile-group-edit-submit" value="<?php _e( 'Save Changes', 'buddypress' ) ?> " />
                <?php
$next_group_id=custom_get_next_group_id();
$prev_group_id=custom_get_prev_group_id();?>
<?php if($prev_group_id):?>
<a href="<?php echo custom_get_group_edit_link($prev_group_id) ;?>" class="button">Previous </a>
<?php endif;?>

<?php if($next_group_id):?>
<a href="<?php echo custom_get_group_edit_link($next_group_id) ;?>" class=" button">Next </a>
<?php endif;?>
    </div>