PHP is a try and guess language.
Drupal Boost Module Caches CSS: Can't Change File After Boost Uninstall
So when working with a dev site, I couldn't figure out why my changes to CSS weren't propagating.
I turned off the boost module, cleared the cache, restarted apache.
Then I realized that Apache must be actually not getting to the file. And the only place to do that in Drupal is the .htaccess file.
Viola! Remove this from your .htaccess:
### BOOST START ###
AddDefaultCharset utf-8
<FilesMatch "(\.html|\.html\.gz)$">
<IfModule mod_headers.c>
Header set Expires "Sun, 19 Nov 1978 05:00:00 GMT"
Header set Cache-Control "no-store, no-cache, must-revalidate, post-check=0, pre-check=0"
</IfModule>
</FilesMatch>
<IfModule mod_mime.c>
AddCharset utf-8 .html
AddCharset utf-8 .css
AddCharset utf-8 .js
AddEncoding gzip .gz
</IfModule>
<FilesMatch "(\.html|\.html\.gz)$">
ForceType text/html
</FilesMatch>
<FilesMatch "(\.js|\.js\.gz)$">
ForceType text/javascript
</FilesMatch>
<FilesMatch "(\.css|\.css\.gz)$">
ForceType text/css
</FilesMatch>
# Gzip Cookie Test
RewriteRule boost-gzip-cookie-test\.html cache/perm/boost-gzip-cookie-test\.html\.gz [L,T=text/html]
# GZIP - Cached css & js files
RewriteCond %{HTTP_COOKIE} !(boost-gzip)
RewriteCond %{HTTP:Accept-encoding} !gzip
RewriteRule .* - [S=2]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css\.gz -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css\.gz [L,QSA,T=text/css]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js\.gz -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js\.gz [L,QSA,T=text/javascript]
# NORMAL - Cached css & js files
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css [L,QSA,T=text/css]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js [L,QSA,T=text/javascript]
# Caching for anonymous users
# Skip boost IF not get request OR uri has wrong dir OR cookie is set OR request came from this server OR https request
RewriteCond %{REQUEST_METHOD} !^(GET|HEAD)$ [OR]
RewriteCond %{REQUEST_URI} (^/(admin|cache|misc|modules|sites|system|openid|themes|node/add))|(/(comment/reply|edit|user|user/(login|password|register))$) [OR]
RewriteCond %{HTTP_COOKIE} DRUPAL_UID [OR]
RewriteCond %{HTTP:Pragma} no-cache [OR]
RewriteCond %{HTTP:Cache-Control} no-cache [OR]
RewriteCond %{HTTPS} on
RewriteRule .* - [S=3]
# GZIP
RewriteCond %{HTTP_COOKIE} !(boost-gzip)
RewriteCond %{HTTP:Accept-encoding} !gzip
RewriteRule .* - [S=1]
RewriteCond %{DOCUMENT_ROOT}/cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html\.gz -s
RewriteRule .* cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html\.gz [L,T=text/html]
# NORMAL
RewriteCond %{DOCUMENT_ROOT}/cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html -s
RewriteRule .* cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html [L,T=text/html]
### BOOST END ###
AddDefaultCharset utf-8
<FilesMatch "(\.html|\.html\.gz)$">
<IfModule mod_headers.c>
Header set Expires "Sun, 19 Nov 1978 05:00:00 GMT"
Header set Cache-Control "no-store, no-cache, must-revalidate, post-check=0, pre-check=0"
</IfModule>
</FilesMatch>
<IfModule mod_mime.c>
AddCharset utf-8 .html
AddCharset utf-8 .css
AddCharset utf-8 .js
AddEncoding gzip .gz
</IfModule>
<FilesMatch "(\.html|\.html\.gz)$">
ForceType text/html
</FilesMatch>
<FilesMatch "(\.js|\.js\.gz)$">
ForceType text/javascript
</FilesMatch>
<FilesMatch "(\.css|\.css\.gz)$">
ForceType text/css
</FilesMatch>
# Gzip Cookie Test
RewriteRule boost-gzip-cookie-test\.html cache/perm/boost-gzip-cookie-test\.html\.gz [L,T=text/html]
# GZIP - Cached css & js files
RewriteCond %{HTTP_COOKIE} !(boost-gzip)
RewriteCond %{HTTP:Accept-encoding} !gzip
RewriteRule .* - [S=2]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css\.gz -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css\.gz [L,QSA,T=text/css]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js\.gz -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js\.gz [L,QSA,T=text/javascript]
# NORMAL - Cached css & js files
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.css [L,QSA,T=text/css]
RewriteCond %{DOCUMENT_ROOT}/cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js -s
RewriteRule .* cache/perm/%{SERVER_NAME}%{REQUEST_URI}_\.js [L,QSA,T=text/javascript]
# Caching for anonymous users
# Skip boost IF not get request OR uri has wrong dir OR cookie is set OR request came from this server OR https request
RewriteCond %{REQUEST_METHOD} !^(GET|HEAD)$ [OR]
RewriteCond %{REQUEST_URI} (^/(admin|cache|misc|modules|sites|system|openid|themes|node/add))|(/(comment/reply|edit|user|user/(login|password|register))$) [OR]
RewriteCond %{HTTP_COOKIE} DRUPAL_UID [OR]
RewriteCond %{HTTP:Pragma} no-cache [OR]
RewriteCond %{HTTP:Cache-Control} no-cache [OR]
RewriteCond %{HTTPS} on
RewriteRule .* - [S=3]
# GZIP
RewriteCond %{HTTP_COOKIE} !(boost-gzip)
RewriteCond %{HTTP:Accept-encoding} !gzip
RewriteRule .* - [S=1]
RewriteCond %{DOCUMENT_ROOT}/cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html\.gz -s
RewriteRule .* cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html\.gz [L,T=text/html]
# NORMAL
RewriteCond %{DOCUMENT_ROOT}/cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html -s
RewriteRule .* cache/normal/%{SERVER_NAME}%{REQUEST_URI}_%{QUERY_STRING}\.html [L,T=text/html]
### BOOST END ###
