chromium/third_party/blink/renderer/core/html/resources/images/selectlist_button_icon.svg

<svg width="20" height="14" viewBox="0 0 20 16" fill="none" xmlns="http://www.w3.org/2000/svg">\
  <path d="M4 6 L10 12 L 16 6" stroke="WindowText" stroke-width="3" stroke-linejoin="round"/>\
</svg>