Dropbox logic is opposite. By default everything gets in sync and you can exclude particular folder out from sync locally using "Selective Sync" feature, per individual install. Individual file cannot be excluded, unfortunately. So, all folders reside on the cloud, but get in locally only those selected (actually contained in selected folders). An alternative is "Smart Sync", but it's not a good idea, I think.
If you need opposite - selected local files residing in Dropbox folder don't get in sync, then use "Ignore" feature. Not very well implemented, but can be applied to folders and/or individual files.