Can I add a text line to a built-in gallery on my home page?

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

Hi

I want to add a text line under the title for each project on my homepage (for a subtitle): 

Add to Design > Custom CSS

a.grid-item[href="/portfolio/employee-welfare-site"] h3:after {
    content: "welfare des";
    display: block;
    font-size: 16px;
}

a.grid-item[href="/portfolio/volunteer-project"] h3:after {
       content: "volunteer des";
    display: block;
    font-size: 16px;
}

a.grid-item[href="/portfolio/bible-study-web-app"] h3:after {
       content: "bible des";
    display: block;
    font-size: 16px;
}

Reference