The count runs to the next January 1 and turns over at your local midnight, so it always matches your own calendar. The thin ring around the date is the current year filling up; when it closes, the count hits zero. For the final minutes, start a timer.
The number is the whole days from today to the next January 1, on your own calendar. Today comes from your device at local midnight, so the count changes when your date changes. On January 1 the page reads "Happy New Year" and the ring around the date has just started again; on January 2 the count is already 364 (365 in a leap year) and heading for the next one.
The page is served without a number. A short script builds January 1 of the current year, moves it a year ahead once that date has passed, and divides the gap from today by 86,400,000 milliseconds, rounding the result. The rounding absorbs the hour a daylight-saving change adds or removes between now and then. It runs again every minute and whenever the tab returns to view. The ring is the current year's elapsed fraction, from January 1 to the next, so the ring closing and the count reaching zero are the same moment.
The new year arrives at each place's own midnight, and so does this page: a reader in Sydney turns over most of a day before a reader in Los Angeles, and each sees the right count for where they are. Nothing is corrected to UTC.
For a countdown to a different date, put it in the address bar as radialtimers.com/countdown-to/YYYY-MM-DD, any date within twenty years either way, for example /countdown-to/2027-01-01, this page's own target. A date the calendar does not have, like February 30, is not a page. The embed snippet below puts the same count on your own site.