Fixed multiple bugs

【Contents of the fix】
■Fixed a bug in which the YouTube video in the top page header content did not play automatically on smartphones.
■Fixed a bug that when the main image is not set in the GALLERY list contents on the top page, the layout of the subsequent contents may collapse.
■Fixed a bug in which the YouTube modal in the “Gallery” section did not work properly when using the Lazyload function.

【Modified file】
front-page.php
functions/acceleration.php
functions/head.php
style.css