Template:Infobox/shared/styles.css

.infobox-header {
    width: 100%;
    padding-top: 15px;
    border-top: 1px solid;
    border-color: var(--border-color-base);
    margin-top: 15px;
    color: var(--color-base--emphasized);
    font-size: 1rem;
    text-align: left;
}