scrollOverflow not 100% width when using "align-items: center" on section

Applying flex + align-items: center will result in the scrollbar of the scrollable section not appearing on the right side of the section/screen as expected.

```css
.section {
  text-align:center;
  font-size: 3em;
  font-family: arial;
  display: flex;
  align-items: center;
}
```

Reproduction:
https://codepen.io/alvarotrigo/pen/myVWYQQ