I'm working on a project using Vue.js and Tailwind CSS and I get this error twice for the same line of code
Unknown at rule @apply css(unknownAtRules)

when using the follwing style
<style scoped>
#home {
@apply bg-accent-gradient;
}
</style>
I found a soultion to add PostCSS Language Support Extensions and the following to my vscode settings
"css.lint.unknownAtRules": "ignore"
I added it but it removed one error only not both.
Make sure you have csstools.postcss extension installed in the VScode before starting debugging the issue as other answers suggested.
I had the same case, I went to vs code settings, searched for Unknown At Rules and select ignore there.

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