Theme takes different css file from /default/files/css when uploaded to remote server from local
The location "default/files/css" is used to store aggregated CSS files, created by Drupal Core. CSS/JS file aggregation can be enabled/disabled by navigating to Drupal Performance settings page, using "Admin => Configure => Development => Performance" and enabling checkbox "Aggregate CSS files". You can also delete the .css files from "default/files/css" directory and Drupal will automatically create new one whenever site is visited first time after that. Check the screenshot below:



It is not advisable on production, but if you want to use original files from Theme's CSS directory directly, then uncheck "Aggregate CSS files" setting checkbox and Try clearing cache.