So here it is:
*:first-child+html {}
But conditional comments are still better.
This post was ported from an old host and CMS, so many comments were lost. Below are the comments that I found were most helpful regarding this post that I salvaged. Some links or attributions may not be working correctly.
Jeff L said:
That’s more than is needed – this will work as well:
*+html { }
where the * = your doctype.