In the web app’s My Files tab, navigate to the location where the folder or file was located.

Click on the following icon to show your deleted files:

In the list of files, you will see your recently deleted files, greyed-out. Right click the folder or files you would like to restore, and select the Restore:

You will then see a confirmation stating your files has been recovered, and the files will appear ‘live’ again:

Now, click the following button again to hide your deleted items: