Today was a happy day, what makes a happy day?

Today was the end of my trip back to my second home, Beppu. So today should have been a rather sad day. But there was this moment during my day today, that I felt super happy and content. I have had those moments regularly ever since I embraced the philosophy of a simple life.
When I was younger, my idea of happy days was grand. It must be a big event, big news, or something out of the ordinary to make my day great. Other than that most days just passed by me. But ever since I started living a more intentional life I have been enjoying most of my days. I am always in a content mood and enjoy the little sparks of joy throughout my day.
Today as I was ending my 8-hour journey back home I reflected upon my trip to Beppu. It was as peaceful as I had imagined. I had no regrets. With this happy state of mind, I came back home and took a nap after lunch.
After waking up I decided to go on my run. Today was the last run of the month. I needed 4km to complete 100km for the month and I did it. It was a great run. But there was this moment during my run that made my day. I was running and making a short video. I was in this park surrounded by trees. The cherry blossoms were in full bloom. There was a slight breeze. It was as if the park was welcoming me back to Toyohashi. At that moment I just stopped and admired the moment. I thanked God. I felt alive and happy. Then I was telling myself how today was a great day, a happy day. Then I started to think about this question.
What makes a happy day? For me a lot of small things make a happy day. Talking to the right person, a bright sunny day, a good run, a good meal, etc. So many small things make my day.
But its not that simple for everyone. So if you are someone who has a different view, do reach out.