Header and menu alignment problems.

First, you need to remove a couple of extra right braces } in your child theme’s style.css file that will cause syntax errors. Change this:

.page-id-247 .entry-title,
.page-id-247 .entry-content p {
  display:  none;}
}
#site-header { text-align: center; }
 #site-header a { display: block; background: #000000; }
}

to this:

.page-id-247 .entry-title,
.page-id-247 .entry-content p {
  display:  none;
}
#site-header { text-align: center; }
 #site-header a { display: block; background: #000000; }

That is, remove the right brace after display: none; and the right brace at the very end of the file.

Then add this to the end:

#site-header, #primary-navigation {
   margin-left: auto;
   margin-right: auto;
   display: table;
   float: none;
}