Flutter, How to remove white spaces around dialog box?

Inside AlertDialog set contentPadding 0

contentPadding: EdgeInsets.zero,

make title to have Container, and add

width: MediaQuery.of(context).size.width,

Then give 0 (or what value you want to have for horizontal patting) to insetPadding like this:

insetPadding: EdgeInsets.symmetric(horizontal: 0),

Below is my example show dialog code, contains alertDialog with horizontal padding = 15 :

Future<void> _showLogoutDialog(BuildContext context) async {
    return showDialog<void>(
      context: context,
      barrierDismissible: true,
      builder: (BuildContext context) {
        return AlertDialog(
          titlePadding: EdgeInsets.only(top: 12, left: 24, right: 12),
          contentPadding: EdgeInsets.only(top: 12, left: 24, bottom: 20),
          insetPadding: EdgeInsets.symmetric(horizontal: 15),
          titleTextStyle: TextStyle(
            color: ColorStyles.primary_blue500,
            fontFamily: 'Muli',
            fontWeight: FontWeight.w500,
            fontStyle: FontStyle.normal,
            fontSize: 16.0,
          ),
          contentTextStyle: TextStyle(
            color: ColorStyles.grey2,
            fontFamily: 'Muli',
            fontWeight: FontWeight.w400,
            fontStyle: FontStyle.normal,
            fontSize: 14.0,
          ),
          title: Container(
            width: screenUsableHeight(context),
            child: Row(
              mainAxisSize: MainAxisSize.max,
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                Text('Log out'),
                IconButton(
                  icon: Icon(
                    Icons.close,
                    color: ColorStyles.grey2,
                    size: 28,
                  ),
                  onPressed: () => Navigator.of(context).pop(),
                  splashColor: Colors.transparent,
                  highlightColor: Colors.transparent,
                  tooltip: "close",
                )
              ],
            ),
          ),
          //EN: Logging out
          content: SingleChildScrollView(
            child: ListBody(
              children: <Widget>[
                Text('Do you want to leave?'),
              ],
            ),
          ),
          actions: <Widget>[
            FlatButton(
              child: Text(
                'Yes',
                style: TextStyle(
                  color: ColorStyles.primary_blue500,
                  fontFamily: 'Muli',
                  fontWeight: FontWeight.w500,
                  fontStyle: FontStyle.normal,
                  fontSize: 16.0,
                ),
              ), //EN: Yes
              onPressed: () {
                _logOut(context);
              },
            ),
            FlatButton(
              child: Text(
                'No',
                style: TextStyle(
                  color: ColorStyles.grey2,
                  fontFamily: 'Muli',
                  fontWeight: FontWeight.w500,
                  fontStyle: FontStyle.normal,
                  fontSize: 16.0,
                ),
              ), //EN: No
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

This looks like:

display of alert dialog

titlePadding: EdgeInsets.zero, contentPadding: EdgeInsets.zero,