I would encourage you to use the Discourse CSS variables about the color because it will work better with dark mode. (you can inspect anything and scroll down)
To center: EDIT: Bryce already answered this!
.discourse-tags {
justify-content: center;
}
color: var(--secondary-low) !important;
background: var(--blend-primary-secondary-5) !important;
You can also use the dark-light-choose(<lightcolor>, <darkcolor>) function to define light and dark colors so the right color will be used when the dark mode is set or not.