how to put down a container in flutter code example

Example: align column to center of flex flutter

// If you want the whole table to be Centered, use the mainAxisAlignment property of Column.
///Column
mainAxisAlignment: MainAxisAlignment.center //Center Column contents vertically,
crossAxisAlignment: CrossAxisAlignment.center //Center Column contents horizontally,

///Row
mainAxisAlignment: MainAxisAlignment.center //Center Row contents horizontally,
crossAxisAlignment: CrossAxisAlignment.center //Center Row contents vertically,