Laravel mix skipping one scss line

I'm developing a Laravel project in Laravel 5.4. I use the Laravel mix package for css, mixing scss files. Today I added to my personal scss file these lines

span.dots-on-overflow {
    overflow: hidden;
    display: -webkit-box;
    -webkit-line-clamp: 5;
    -webkit-box-orient: vertical;
}

but after mixing the result I had is only

span.dots-on-overflow {
    overflow: hidden;
    display: -webkit-box;
    -webkit-line-clamp: 5;
}

I don't understand the reason why the line -webkit-box-orient: vertical; is missing, or maybe skipped.

The css has no errors since I pasted it from the style attribute in html.

Thanks in advance if you can help!

via Chebli Mohamed