Reply To: Add social icons and change header border color.

1)

.site-header {
    border-left: 1px solid #e9e9e9;
    border-right: 1px solid #e9e9e9;
    border-top: 1px solid #e9e9e9;
}

Change the hex color to your choice

2) Just change the images in img folder inside theme folder keeping the same image names. Then drop the folder in the child theme.

3) Modifying the options page would require custom work.
But you can modify header.php to add github icon easily.

Line 70 and 71 of header.php is (just below class rss)

<?php } ?>
</div>

Add your github image code html inside it:

<?php } ?>
github html here
</div>