EE doesn't seem to be parsing {snippet} tags inside a template of type stylesheet - I'm guessing because the curly braces conflict with CSS's own braces indicating the start of a style declaration. Is there a way to sort of escape these characters or something?
Ex:
.style { /* CSS curly brace */
width: {snippet_width}px; /* EE curly brace */
}
While use cases for it are rare, CSS templates can parse tags if you need them to, but you must link to them with {path='template_group/css_template'} instead of {stylesheet='template_group/css_template}.
EE's CSS and JS templates do not parse variables or tags. They're just static templates. Best to avoid EE altogether and just create CSS and JS files on the server. To still be somewhat dynamic, you can always hard-code rules in the <head> (for CSS) or above </body> (for JS). For example:
<style>
.style {
width: {snippet_width}px;
}
</style>
