Css issue

for the first question I wanted to make the pin post to a direct link to a hashtag page as this post discussed: Active link to other webpage in Pinned Post on landing page? - #7 by cjeller1592
but there’s no ‘Custom Javascript’ opinion on the backstage. I don’t know if there’s a way to modify only with the css code.

for the other two questions I just don’t know how to call those parameters. How the css code define the grey line which separates the articles and footer area?
I changed the width of the article and footer area like below, but the grey line is not included.
And how to move the paging indicator (older/newer) aligned with the width of the article?

#wrapper, #collection article, #post article, #subpage article{
max-width: 720px !important;
margin-top: 0px !important;
margin-bottom: 75px !important;
padding-right: 0px !important;
padding-left: 0px !important;
line-height: 24PX !important;
margin-right: auto; /* 1 /
margin-left: auto; /
1 */
}

body footer, nav #page {
max-width: 1100px !important;
margin-right: auto; /* 1 /
margin-left: auto; /
1 */
text-align: center;
padding: 0 2em;
background-color: #f6f6f6;

Here is the post:ハンミョウ — 写意 Writee

The third question is that how can I change the font size of the hashtag on top of the each hashtag page?