The custom CSS snippets can be added to Appearance -> Customize -> Additional CSS
For mobile:
/* Change slide headings font size on mobile */
@media (max-width: 991px) {
.jumbotron .jumbotron-caption .caption-small-heading {
font-size: 14px;
}
.jumbotron .jumbotron-caption .caption-heading .caption-heading-tag {
font-size: 32px;
}
}
The 14px and 32px values can be changed to your own needs.
For desktop:
/* Change slide headings text size on dekstop */
@media (min-width: 992px) {
.jumbotron .jumbotron-caption .caption-small-heading {
font-size: 15px;
}
.jumbotron .jumbotron-caption .caption-heading .caption-heading-tag {
font-size: 40px;
}
}
The 15px and 40px values can be changed to your own needs.