To do so, you have to target the `eye-left` HTML element by its `id` thanks to the [`getElementById`](https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById) method. Then, [change the `style`](https://developer.mozilla.org/en-US/docs/Web/API/ElementCSSInlineStyle/style#setting_styles) of your `eye-left` to set its background color to black. We also need to modify its shape ; for that we are going to add a new class to it.
In the JS file, add the freshly-created class `eye-closed` to the [`classList`](https://css-tricks.com/snippets/javascript/the-classlist-api/) of your `eye-left` element, and [set its style property](https://developer.mozilla.org/en-US/docs/Web/API/ElementCSSInlineStyle/style#setting_styles) background color to "black".