[css-table-3][css-backgrounds] tr background-color when td cell has a border-radius

[karlcow]

Should the tr element background-color be painted or not in this case?
Should it be specified in (is it already?)
https://drafts.csswg.org/css-backgrounds/
or in https://drafts.csswg.org/css-tables-3/

https://codepen.io/webcompat/pen/xbxwmJr

• Safari and Chrome do not show the background-color of the tr element
• Firefox does show the background-color (pink) of the tr element

code

<style>
table {background-color: gold;}
tr    {background-color: pink;}
td    {background-color: rgb(76, 250, 188);}
td {
  width:50px;
  height:50px;
  border-color: red;
  border-width: 10px;
  border-radius: 30px;
  border-style: solid;}
</style>
<table>
  <tr><td>A1</td><td>A2</td><td>A3</td></tr>
  <tr><td>B1</td><td>B2</td><td>B3</td></tr>
  <tr><td>C1</td><td>C2</td><td>C3</td></tr>
</table>

rendering

[Loirooriol]

https://drafts.csswg.org/css2/#table-layers

the background covers exactly the full area of all cells that originate in the row, even if they span outside the row

So if border-radius shrinks the area of the cells, then the background of the row should only be painted in that shrunken area.

Servo matches Blink and WebKit, BTW.

[karlcow]

There are missing WPT for tables covering this scenario it seems.
Or maybe I didn't find them.

[karlcow]

At the beginning of table layers it says

The background set on an element in one of the layers will only be visible if the layers above it have a transparent background.

In 4.6. Effect on Tables, it says:

The border-radius properties do apply to table, inline-table, and table-cell boxes in separated borders mode (border-collapse: separate). When border-collapse is collapse, they have no effect.

I wonder why the area of the table cell outside of the border is not considered transparent.

https://codepen.io/webcompat/full/MYWKbrm