Is there an existing issue for this?

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Is your feature request related to a problem? Please describe the problem.

If you use display:flex on a scroll container, then its child elements will by default automatically shrink to the size of their content even if you have height: someLargeValue. To avoid this you must specify flex-shrink:0 for the child elements.

The Virtualize component is adversely affected by this, because its placeholders contain no content, and therefore by default will shrink to zero height if you have display:flex on the container. This was reported at #40123

Describe the solution you'd like

The generated placeholder elements should have flex-shrink: 0 automatically. As far as I'm aware, there's no drawback in doing this even when the parent isn't display:flex, because it would just be ignored in that case.

We could either do this on the JS side by adding the style automatically inside the mutation observer (like we already apply the display: table-row style automatically in some cases). Or we could do it on the .NET side by hardcoding flex-shrink: 0 into the style attribute that we already generate for the height.

Additional context

Until this is done, it would be helpful to add a note to the docs about it. PR: dotnet/AspNetCore.Docs#25041