yup… that .htaccess is preventing access as mentioned… wp does not put an .htaccess file there… wp-content is the storage location for plugins and themes if needed… even the uploaded files for posts are there (though handled differently)..
as to php, that is a fine way (somewhat non standard but allowed) to display css… the file gets parsed and generates valid css to control display… as mentioned, some servers disallow it (by default it is allowed) but no one knows why.. but that is why we provide css only styles too… which I have asked you to try…
so you have two options… 1) remove the .htaccess (neither wp or sp put it there).. 2) switch to a non php, css only sp theme (as discussed)… there is css only or barebones css (desktop and mobile)…
downside to css only themes is you can not use simple php color overlays to offer lots of colorization options…