TYPO3 Core

Tried with the following TypoScript:

config.compressCss = 1
page.cssInline {
    10 = TEXT
    10.value = body {background:lime;}

    20 = TEXT
    20.value = h1 {color: blue;}
}

This creates an external file with .gzip and that content, because of inlineStyleToTempFile. Next I tested with:

config.inlineStyle2TempFile = 0
config.compressCss = 1
page.cssInline {
    10 = TEXT
    10.value = body {background:lime;}

    20 = TEXT
    20.value = h1 span {color: blue;}
}

which results in:

<style type="text/css">
/*<![CDATA[*/
<!-- 
/*additionalTSFEInlineStyle*/
body {background:lime;}h1 span {color: blue;}
-->
/*]]>*/
</style>

which looks fine to me.

How to reproduce your issue? How do you add your inline CSS?

Patch set 1 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/63884

Applied in changeset 72345298ec7cbe3f354d64c32fee6cef61223bda.