html validation error rotate property

Hello.

I am new to WordPress and web development.

I have just finished to develop a site using TT4 theme and FSE customization (https://www.seotesting.site) , and I am getting trouble when validating my html. I have used the Nu html checker tool as recommended in this article https://codex.wordpress.org/Validating_a_Website, and the checker points out several errors in my code, among them two errors regarding the rotate property, within the inline CSS for the paragraph block and the heading block.

I don’t see any problem in the code, any idea why the validation failed?

Here are the errors  showing after the validation :

• CSS: rotate: Property rotate doesn’t exist.

From line 47, column 635; to line 47, column 640

"]{rotate:180deg}

• CSS: rotate: Property rotate doesn’t exist.

From line 58, column 1009; to line 58, column 1014

]){rotate:180deg}↩↩