I found the location to be from:
wp-content/plugins/wp-splash-page/templates/default/style.css
body, #wpsp-continue, #wpsp-month, #wpsp-day, #wpsp-year {
font: <strong>22px</strong> Arial, Helvetica, sans-serif;
line-height: 1.4em;
text-align: <strong>center</strong>;
}
