Change portfolio items text colour on mobile

Site URL: https://www.kimbalbumstead.com/projects

Hello,

I would like to change the text colour of portfolio items from black to white for mobile viewing.

I have tried this code  in Design>Custom CSS but it doesn't work. 

@media screen and (max-width:640px) {
.portfolio-text {
    color: #000000 !important;
}
}

What would be the correct code?

Many thanks 

Add to Design > Custom CSS

/* Mobile portfolio title color */
@media screen and (max-width:767px) {
h3.portfolio-title {
    color: white !important;
}}

@tuanphan Ah great, thank you that works 🙂