Placeholder Avatar

import 'package:flutter/material.dart';

Container(
  width: 48,
  height: 48,
  decoration: BoxDecoration(
    shape: BoxShape.circle,
    color: Colors.grey.shade300,
  ),
  alignment: Alignment.center,
  child: Icon(
    Icons.person,
    size: 30,
    color: Colors.grey.shade600,
  ),
),