Bug fixes / Support for WP5.8 widget block editor

【Contents of the fix】
■Fixed a bug that the category and date were not displayed in the blog list on the fixed page.
■Support for the WordPress 5.8 widget block editor
■Minor bug fixes

【Modified files】
admin/css/my_admin.css
admin/inc/basic.php
css/responsive.css
functions/page_ad_post_list.php
template-parts/sns-btn-btm.php
template-parts/sns-btn-top.php
functions.php
style.css