Project: selector
Task (challenging): modify css for elements in `#table`:
- append in cell(1,3) with: 
  `<form>
    <input type="text" disabled />
    <input type="text" />
    <input type="text" required />
    <button type="submit">Submit</button>
  </form>` 
  - set enabled control `background-color` to `green`
  - set disabled control `background-color` to `yellow`
  - suffix the required control with a red `*`
  - set invalid control `background-color` to `red`
- do not use `!important` anytime