<scrollbar-width>

Defines the width of the scrollbar as a keyword. It must be one of the following values:

auto	The default scrollbar width for the platform.
thin	A thin scrollbar width variant on platforms that provide that option, or a thinner scrollbar than the default platform scrollbar width.
none	No scrollbar shown, however the element will still be scrollable.

Note: User Agents must apply any scrollbar-width value set on the root element to the viewport.

Use this property with caution — setting scrollbar-width to thin or none can make content hard or impossible to scroll if the author does not provide an alternative scrolling mechanism. While swiping gestures or mouse wheels can enable scrolling on such content, some devices have no scroll alternative.

WCAG criterion 2.1.1 (Keyboard) has been in place for a long time to advise on basic keyboard accessibility, and this should include scrolling of content areas. And introduced in WCAG 2.1, criterion 2.5.5 (Target Size) advises that touch targets should be at least 44px in width and height (although the problem is compounded on high-resolution screens; thorough testing is advised).

• MDN Understanding WCAG, Guideline 2.1 explanations
• MDN Understanding WCAG, Guideline 2.5 explanations
• Understanding Success Criterion 2.1.1 | W3C Understanding WCAG 2.1
• Understanding Success Criterion 2.5.5 | W3C Understanding WCAG 2.1

scrollbar-width = 
  auto  |
  thin  |
  none  

CSS

.scroller {
  width: 300px;
  height: 100px;
  overflow-y: scroll;
  scrollbar-width: thin;
}

HTML

<div class="scroller">
  Veggies es bonus vobis, proinde vos postulo essum magis kohlrabi welsh onion
  daikon amaranth tatsoi tomatillo melon azuki bean garlic. Gumbo beet greens
  corn soko endive gumbo gourd. Parsley shallot courgette tatsoi pea sprouts
  fava bean collard greens dandelion okra wakame tomato. Dandelion cucumber
  earthnut pea peanut soko zucchini.
</div>

Result

• ::-webkit-scrollbar