body {
  font-family: "Times New Roman";
}

#noidung {
  width: 400px;
  margin: 30px auto;
}

h3 {
  text-align: center;
  margin-bottom: 15px;
}

.dong {
  margin: 5px;
}

input[type="text"] {
  width: 230px;
}

#vitri {
  width: 80px;
}

.nut {
  text-align: center;
  margin: 5px;
}

button {
  font-size: 11px;
}