Multiple bug fixes

【Contents of the fix】
■Fixed a bug that CSS may not be applied when accessing pages that are still http (mixed content) when using the CSS code optimization function under SSL environment.
■Fixed a bug that images set to “Background image (for mobile)” of fixed pages are not reflected.
■【iPhone】Fixed an issue where the Hatena bookmark icon does not appear on the share button in the fixed footer bar.

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

【Modified file】
css/footer-bar.css
css/responsive.css
functions/acceleration.php
page-lp.php
page.php
style.css
template-parts/footer-bar.php

【Added files】
img/common/hatenabookmark-logomark.svg