Overflow-y: scroll; on side navigation prevents tooltip functionality

I have a side navigation with the following styles

position: fixed;
left: 0;
top: 0;
height: 100%;
width: 78px;
background: #11101D;
padding: 6px 14px;
z-index: 99;
transition: all 0.5s ease;
overflow-x: visible;
overflow-y: scroll;

Which allows the user to scroll vertically on the side navigation.

When a user hovers on a navigation item, a tooltip appears to the right.

position: absolute;
top: -20px;
left: calc(100% + 15px);
z-index: 3;
background: #fff;
box-shadow: 0 5px 10px rgba(0, 0, 0, 0.3);
padding: 6px 12px;
border-radius: 4px;
font-size: 15px;
font-weight: 400;
opacity: 0;
white-space: nowrap;
pointer-events: none;
transition: 0s;

However, because of the overflow-y: scroll; on the parent, it doesn’t overlap the sidebar, instead you scroll horizontally to see it, which isn’t desired.

Current Tooltip

on hover
on hover and vertical scroll

Desired Tooltip (with side nav scroll functionality)

tooltip visible with scroll

I have a JSFiddle with all the markup and styles.

I want the the side nav to be vertically scrollable while still having the functionality to view the tooltip.

Any help would be greatly appreciated. This is based on a React Application, so would prefer non JQuery solutions.