There are a lot of CSS errors.
And the usual assortment of vendor prefix stuff.
But the font rules look to all be under the valid section AFAICT
https://jigsaw.w3.org/css-validator/validator?uri=https%3A%2F%2Ftangtocmaytinh.blogspot.com&profile=css3&usermedium=all&warning=1&vextwarning=&lang=en