.govuk-phase-banner__content.custom-font-size,
.govuk-phase-banner__content__tag.custom-font-size {
    font-size: 1.4rem;
}

/* Desktop (GOV.UK breakpoint) */
@media (min-width: 40.0625em) {
    .govuk-phase-banner__content.custom-font-size,
    .govuk-phase-banner__content__tag.custom-font-size {
        font-size: 1.6rem;
    }
}