[docs beta] "Scrolling to an element" example does not work on Safari

Checking the beta docs, I noticed that one of the examples was not working. At first it was not working at all, but after I added a style of overflow-x: auto to the <ul> element, then I could see the desired effect after clicking on the buttons. I could later check that the example works as expected (without any changes in Chrome). My first guess is that Safari doesn't scroll because the element has an implicit overflow as visible.

Please note that this issue is also present on the challenge 3, as it basically uses that same principle to scroll the images.

Steps

1. Open https://beta.reactjs.org/learn/manipulating-the-dom-with-refs#example-scrolling-to-an-element on Safari
2. Click on the buttons

先在 Safari 中重現 React beta 文件「Scrolling to an element」區段的範例，然後將其與使用相同捲動原理的 challenge 3 進行比較。調查回報的 overflow 行為，並確認點擊兩個範例中的按鈕時，它們都能如預期運作，而不需要手動變更樣式。