Center text under image blocks

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

Hello all,

Very new to the platform. I tried searching and couldn't find the fix for what I am trying to do. On my homepage, I cannot figure out how to get the text under the 3 images just below the banner to be center aligned. When in the text edit mode there is only the option to bold, italicize or link the text.

Thanks in advance!

Add to Home > Design > Custom CSS

/* text under banner */
@media screen and (max-width:640px) {
div#page-5f8062a31bd8945aecb0eb5e .image-subtitle {
    text-align: center;
}
}