This is LocalDB, not exactly SQL Server Express.  If it was Express the connection string would look similar to what your production one needs to be.  LocalDB works more like a desktop file based DB, more like MS-Access than SQL Server.  For production purposes, your connection string will look very different.
Take a look at this site that shows you various methods of writing your connection strings depending on what connection library you are using:
https://www.connectionstrings.com/sql-server/