Custom theme not Working on WordPress multiple sites

I Install Network in WordPress for multi site and followed installation process from codex.

But now problem is that my custom theme is not working and also i can’t see the add theme option.

.htaccess:

RewriteEngine On
RewriteBase /demo/youcubed/
RewriteRule ^index.php$ - [L]

RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $ [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*.php)$ $2 [L]
RewriteRule . index.php [L]

WP-config:

define( 'WP_ALLOW_MULTISITE', true );

define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'socialgummers.com');
define('PATH_CURRENT_SITE', '/demo/youcubed/');
define('SITE_ID_CURRENT_SITE', 1);

define('BLOG_ID_CURRENT_SITE', 1);