Wordpress Permalinks Causing Issues With Stylesheet?

One of my client's sites (located at americanindustrialinc.com/wp) is having problems with permalinks.

Every time i change the permalink settings to anything other than 'default' the stylesheet goes completely out the window.
This is an ad that I inserted!
I have tried everything i could possibly think of (which wasnt much, to be honest) and nothing is working. I have also posted this issue on several other forum sites trying to get help but have not gotten any help whatsoever.

I'm not sure what information may be needed so here is some general background info:

the client's site is self-hosted on a windows server running IIS 11.
They have a pre existing site on this server built with ASP
I built the wordpress site in a subdirectory.
I know nothing about ASP or windows servers.

THE ODD PART:
when viewing in IE9 it looks normal. the stylesheet appears to be funtioning perfectly fine.
I use a Mac,, so when i test for IE i use Parallels.
I do not have the ability to test from an actual PC.

Any browser on Mac (safari, chrome , FF) are all showing the same issue.
Even Opera Mini on android is showing the same issue.

when permalinks are set to 'default' the site looks precisely as it should (ignoring the issues with the navigation)

When i change the permalinks to anything other than 'default' it looks like this:

Anybody know what could be causing this?
I have never encountered something like this before.

I have checked:
path to stylesheet
(its the wordpress default php method, but i have also tried 'hard-coding' it in HTML, with, unsurprisingly, no difference. I have tried both relative and absolute paths with no difference.)
web.config file (it appears to be perfectly normal)
re-installing the theme
re-installing WP core
disabling plugins
reinstalling plugins
browser cache
pretty much all the basic things you would check when you have no idea whats going on.

Thats all i can come up with for now.
If you need further intel, simply ask.

I greatly appreciate any and all help!

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