I am currently developing a custom theme, one day my css assets completely stopped working and couldn’t be loaded at all in my theme. I didn’t change anything, it used to work just fine.
Are you running this theme locally on your machine (via the Shopify CLI) or in a live Shopify store? If you’re using the Shopify CLI - which version are you running? You may need to update to the most recent version.
Can you also check if JS files are also not working with a console.log message?