Why does this flex-container overflow?

I have a flex-container with a fractional pixel width with 8 flex-children. I expect the container to not overflow, but it does.

• The browser is Chrome or Edge on Windows. (Not in Firefox.)
• The container has width of xxx.45px.
• There are exactly 8 children; they have flex: 1. (1-7 children works as expected.)
• It only occurs on my secondary screen with screen scaling 100%, not on the primary with 125%.

The code:

.d1 {
  display: flex;
  overflow: auto;
  height: 100px;
  width: 100.45px;
}

.d1 > * {
  flex: 1;
  border: 1px solid blue;
}

<div class="d1">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

On Chrome and Edge I see a horizontal scollbar that I don't see on Firefox. The calculated widths are not what I expect either; the parent is 240.438px wide (I expected 240.45px) and each child is 30.063px wide (meaning the sum is 240.504px).