React

HTML

<div id="app"></div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

.done {
  color: rgba(0, 0, 0, 0.3);
  text-decoration: line-through;
}

input {
  margin-right: 5px;
}

React

const makeRandomColorStyle = () => {
  const getColor = () => Math.floor(Math.random() * 255);
  return {
    color: `rgb(${getColor()},${getColor()},${getColor()})`,
    backgroundColor: `rgb(${getColor()},${getColor()},${getColor()})`,
  };
};

class TodoApp extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
      items: [
        {text: "Learn JavaScript", done: false},
        {text: "Learn React", done: false},
        {text: "Play around in JSFiddle", done: true},
        {text: "Build something awesome", done: true}
      ]
    }
    setInterval(() => {
      this.setState({
        items: [
          {text: "Build something awesome", done: true}
        ]
      })
    }, 500)
  }

  render() {
    return (
      <div style={makeRandomColorStyle()}>
        <h2>Todos:</h2>
        <ol>
          {this.state.items.map(item => (
            <li key={item.id}>
              <label>
                <input type="checkbox" disabled readOnly checked={item.done}/>
                <span className={item.done ? "done" : ""}>{item.text}</span>
              </label>
            </li>
          ))}
        </ol>
      </div>
    )
  }
}

ReactDOM.render(<TodoApp/>, document.querySelector("#app"))