I don’t like mixing tenses, either:
“a website”...”their”
maybe “its” would be better
a website...their
maybe its would be better
The distinction is whether "website" is being used as a count noun or as a mass noun. I treated it as a count noun, though most, I acknowledge, would treat it as a mass noun.
In either case, however, "website" and "their" are not verbs, and therefore do not have tenses.
p.s. I had to look all that up, so perhaps I was just lucky.