Bug with hardcoded wp-content/plugins

Line 9 at highlighter.php contain hardcoded path

$themeDir = ABSPATH . '/' . ($wp_sh_use_theme ? ($wp_sh_use_theme) : ('wp-content/plugins/wp-synhighlight/themes/default'));

and plugin is broken when used with moved wp-content folder.

You should use WP_PLUGIN_DIR instead hardcoded path

https://wordpress.org/plugins/wp-synhighlight/