For folders I've selected under selective sync, I want them to be available offline on the PC. Right now, I see the folders and files on the PC, but the icons are gray and I can't open then when offline.
Solved: as commenter mentioned, you have to right click the folders (can select multiple folders at a time ) and select smart sync -> local
When you selectively sync a folder, you remove it from your hard drive, but not from your account.
For this reason, if you want them available on your computer, ensure that you haven't chosen them to be selective synced.
Once they are downloaded locally, you can access the content even if your desktop app isn't running. Please note though that any updates you make inside your Dropbox folder won't be applied to your account until you launch the desktop app again.