Say Hello in Dart

index.html

<h1>Hello, <span id="name"></span></h1>
<input type="text" id="name_box">
<input type="submit" value="Say Hello" id="button">

main.dart

import 'dart:html';
void main() {
 querySelector("#button").onClick.listen(sayHello);
}
void sayHello(MouseEvent event) {
 querySelector("#name").text = (querySelector("#name_box") as InputElement).value;
 (querySelector("#name_box") as InputElement).value = "";
}

styles.css

html, body {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
}

#wrapper {
  width: 300px;
  margin: auto;
  border: solid thin black;
}