When clicking on the card in Flutter, I want to give a border color and the card can be selected

 Container(
          height: 80,
          width: 80,
          child: Card(
            color: Color.fromARGB(255, 19, 85, 144),
            child: Center(
                child: Text(
              widget.title,
              style: GoogleFonts.poppins(
                  color: Colors.white,
                  fontSize: 20,
                  fontWeight: FontWeight.bold),
            )),
          ),

For example, when the card number 9 is clicked, as in the image, I want a red border around it.

>Solution :

first, declare a boolean variable at the top of that widget:

bool isSelected = false;

then set the border on the container based on that bool:

 Container(
      height: 80,
      width: 80,
      decoration: BoxDecoration(
       border: isSelected ? Border.all(color: Colors.red, width: 2,) : null
       ),
      child: Card(
        color: Color.fromARGB(255, 19, 85, 144),
        child: Center(
            child: Text(
          widget.title,
          style: GoogleFonts.poppins(
              color: Colors.white,
              fontSize: 20,
              fontWeight: FontWeight.bold),
        )),
      ),

then wrap your widget with GestureDetector widget, toggle that isSelected in the onTap method property, and update the state

 GestureDetector(
    onTap: () {
    isSelected = !isSelected;
    SetState(() {});
    },
    child: Container(
          height: 80,
          width: 80,
          decoration: BoxDecoration(
           border: isSelected ? Border.all(color: Colors.red, width: 2,) : null
           ),
          child: Card(
            color: Color.fromARGB(255, 19, 85, 144),
            child: Center(
                child: Text(
              widget.title,
              style: GoogleFonts.poppins(
                  color: Colors.white,
                  fontSize: 20,
                  fontWeight: FontWeight.bold),
            )))),