Changing subhead in Portfolio grid template

Site URL: https://www.adaloongdesign.com/

I am currently working on my portfolio and I figured out how to add subhead text in the portfolio grid template. But, I want to change the color of the subhead text to black. I tried adding "color: black;" in css but it doesn't seem to change. What is the correct way to change the color of the text?

Reference image below on how implemented the CSS

Use this CSS to change all sub texts to black

a.grid-item h3:after {
    color: black !important;
}