.htaccess returning broken images with 500 (Internal Server Error)

Question

i am using phppenny auction, however they closed down recently, i am having a hard time understand their file structure since the documentation is not accessible,

and there is alot of images files / js files / css files return 500 error in the console log but when i try to access the files directly from the absolute path, it is fine. i have no idea why it doesn't manage to render as a whole in the tag, same goes to the images.

i'm thinking that the .htaccess causing the problems, but i am not certain

public_html/.htaccess :

<IfModule mod_rewrite.c>
RewriteEngine on 
RewriteRule    ^$ webroot/    [L]
RewriteRule    (.*) webroot/$1 [L]
</IfModule>

Options -Indexes

<files .htaccess>
order allow,deny
deny from all
</files>

public_html/webroot/.htaccess

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?url=$1 [QSA,L] 
</IfModule>

any help will be deeply appreciated, i won't mind paying a small token of appreciation to resolve this issue, as it been trouble me for days.