Black Gradient shows white in portfolio grid overlay.

Site URL: https://shark-clementine-5jph.squarespace.com/portfolio

.portfolio-overlay {
      background: linear-gradient(to bottom, #ffffff00 50%, #000000)}

I'm trying to have a black gradient that fades to transparent on the portfolio grid overlay. But the existing overlay prevents #FFFFFF00 from being transparent (it's just showing as white (#FFFFFF).

Any help is greatly appreciated. And please let me know if I can provide any other info. I'll be sure to get back right away. 

Site password is: mz

.portfolio-overlay {
    background: linear-gradient(to bottom, #fff0 0 50%, #000) !important;
}