<field
	type="filelist"
	filter="^(theme_)[A-Za-z0-9]*(.css)"
name="stylefiles"
hide_default="true"
hide_none="true"
multiple="false"
default="default.css"
directory="modules/mod_select/css/"
exclude=""
stripext=""
label="Style">
</field>

Not working filter files
filter="^(theme_)[A-Za-z0-9]*(.css)"
filter="css"
filter="^(?!(theme_*)|(default.css)|(test.css)).*.css"
filter="^(?!(forAdmin.css)|(test.css)).*.css"
filter="^(?!forAdmin.css).*.css"

Display all files in directory