When I don't use Munee, I don't have these problems...
My CSS file have not this problem.
Here is my .htaccess, if you need it...
# ##############################################################################
# # ERRORS #
# ##############################################################################
# ------------------------------------------------------------------------------
# | 404 error prevention for non-existing redirected folders |
# ------------------------------------------------------------------------------
Options -MultiViews
# ------------------------------------------------------------------------------
# | Custom error messages / pages |
# ------------------------------------------------------------------------------
ErrorDocument 404 /404.html
# ##############################################################################
# # MIME TYPES AND ENCODING #
# ##############################################################################
# ------------------------------------------------------------------------------
# | Proper MIME types for all files |
# ------------------------------------------------------------------------------
<IfModule mod_mime.c>
# Audio
AddType audio/mp4 m4a f4a f4b
AddType audio/ogg oga ogg opus
# Data interchange
AddType application/json json map
AddType application/ld+json jsonld
# JavaScript
# Normalize to standard type.
# http://tools.ietf.org/html/rfc4329#section-7.2
AddType application/javascript js
# Video
AddType video/mp4 f4v f4p m4v mp4
AddType video/ogg ogv
AddType video/webm webm
AddType video/x-flv flv
# Web fonts
AddType application/font-woff woff
AddType application/vnd.ms-fontobject eot
AddType application/x-font-ttf ttc ttf
AddType font/opentype otf
# Make SVGZ fonts work on the iPad.
# https://twitter.com/FontSquirrel/status/14855840545
AddType image/svg+xml svgz
AddEncoding gzip svgz
# Other
AddType application/octet-stream safariextz
AddType application/x-chrome-extension crx
AddType application/x-opera-extension oex
AddType application/x-web-app-manifest+json webapp
AddType application/x-xpinstall xpi
AddType application/xml atom rdf rss xml
AddType image/webp webp
AddType image/x-icon cur
AddType text/cache-manifest appcache manifest
AddType text/vtt vtt
AddType text/x-component htc
AddType text/x-vcard vcf
</IfModule>
# ------------------------------------------------------------------------------
# | UTF-8 encoding |
# ------------------------------------------------------------------------------
AddDefaultCharset utf-8
<IfModule mod_mime.c>
AddCharset utf-8 .atom .css .js .json .jsonld .rss .vtt .webapp .xml
</IfModule>
# ##############################################################################
# # URL REWRITES #
# ##############################################################################
# ------------------------------------------------------------------------------
# | Rewrite engine |
# ------------------------------------------------------------------------------
<IfModule mod_rewrite.c>
Options +FollowSymlinks
# Options +SymLinksIfOwnerMatch
RewriteEngine On
# RewriteBase /
</IfModule>
# ##############################################################################
# # SECURITY #
# ##############################################################################
# ------------------------------------------------------------------------------
# | File access |
# ------------------------------------------------------------------------------
<IfModule mod_autoindex.c>
Options -Indexes
</IfModule>
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
<IfModule mod_rewrite.c>
RewriteCond %{SCRIPT_FILENAME} -d [OR]
RewriteCond %{SCRIPT_FILENAME} -f
RewriteRule "(^|/)\." - [F]
</IfModule>
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
<FilesMatch "(^#.*#|\.(bak|config|dist|fla|in[ci]|log|psd|sh|sql|sw[op])|~)$">
# Apache < 2.3
<IfModule !mod_authz_core.c>
Order allow,deny
Deny from all
Satisfy All
</IfModule>
# Apache = 2.3
<IfModule mod_authz_core.c>
Require all denied
</IfModule>
</FilesMatch>
# ##############################################################################
# # WEB PERFORMANCE #
# ##############################################################################
# ------------------------------------------------------------------------------
# | Compression |
# ------------------------------------------------------------------------------
<IfModule mod_deflate.c>
<IfModule mod_setenvif.c>
<IfModule mod_headers.c>
SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
</IfModule>
</IfModule>
<IfModule mod_filter.c>
AddOutputFilterByType DEFLATE application/atom+xml \
application/javascript \
application/json \
application/ld+json \
application/rss+xml \
application/vnd.ms-fontobject \
application/x-font-ttf \
application/x-web-app-manifest+json \
application/xhtml+xml \
application/xml \
font/opentype \
image/svg+xml \
image/x-icon \
text/css \
text/html \
text/plain \
text/x-component \
text/xml
</IfModule>
</IfModule>
# ------------------------------------------------------------------------------
# | Expires headers |
# ------------------------------------------------------------------------------
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 1 month"
# CSS
ExpiresByType text/css "access plus 1 week"
# Data interchange
ExpiresByType application/json "access plus 0 seconds"
ExpiresByType application/ld+json "access plus 0 seconds"
ExpiresByType application/xml "access plus 0 seconds"
ExpiresByType text/xml "access plus 0 seconds"
# Favicon (cannot be renamed!) and cursor images
ExpiresByType image/x-icon "access plus 1 week"
# HTML components (HTCs)
ExpiresByType text/x-component "access plus 1 month"
# HTML
ExpiresByType text/html "access plus 0 seconds"
# JavaScript
ExpiresByType application/javascript "access plus 1 week"
# Manifest files
ExpiresByType application/x-web-app-manifest+json "access plus 0 seconds"
ExpiresByType text/cache-manifest "access plus 0 seconds"
# Media
ExpiresByType audio/ogg "access plus 1 month"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType video/mp4 "access plus 1 month"
ExpiresByType video/ogg "access plus 1 month"
ExpiresByType video/webm "access plus 1 month"
# Web feeds
ExpiresByType application/atom+xml "access plus 1 hour"
ExpiresByType application/rss+xml "access plus 1 hour"
# Web fonts
ExpiresByType application/font-woff "access plus 1 month"
ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
ExpiresByType application/x-font-ttf "access plus 1 month"
ExpiresByType font/opentype "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
</IfModule>
#### Munee .htaccess Code Start ####
RewriteRule ^(.*\.(?:css|less|scss|js|coffee|jpg|png|gif|jpeg))$ munee.php?files=/$1 [L,QSA,NC]