For 5250 (AS400 / iSeries / IBM i) Hosts enter the name of the stylesheet file (.css extension) to be used as the default stylesheet for new emulation users.
If you have configured your cssx keys to provide a selection of stylesheets, the value of TN5250CSS should match the CfgName of one of the stylesheets you have defined.
If this setting is missing, the termCSS setting will be used for 5250.