Multiple bug fixes

【Contents of the fix】
■Fixed a bug where YouTubed video tags could not be used in fixed page templates.
■Fixed a bug that when using the quick tag “Layout 3c”, there would be a blank space on the right side of the screen when displayed on a smartphone.
■Fixed a bug that caused the right side of the screen to be blank when using the quick tag “Layout 3c”.

The following are the files that have been modified for this update.

【Modified file】
css/responsive.css
page-design1.php
page-design2.php
page-design3.php
style.css
template-parts/sns-btn-btm.php
template-parts/sns-btn-top.php