::-webkit-scrollbar {
height: 4px; /* height of horizontal scrollbar ← You're missing this */
width: 4px; /* width of vertical scrollbar */
border: 1px solid #d5d5d5;
}
Since logically one cannot force a vertical scrollbar to be a certain height (since dictated by the positioned parent)
Therefore such height property is to target the horizontal's scrollbar height
and vice-versa (width for the width of the vertical scrollbar).