Finally this project is done!
I call it "Surprise Box". The Box I created has several layers.
The lower layer is used to hide Arduino and battery. I also make a hold at the bottom of the heart, in order for a LED light to go in.
The Arduino part of my project, I used a PIR sensor, so when people approach the box or when people open it, the heart will be light up.

Another thing is the "fence" that's built inside the box by a wall of hexagons, which created an empty space inside, was supposed to be used for planting. My original idea was to plant some moss in the box as a background. However, I haven't found moss to plant there yet, so I used some dry pine tree leaves instead.

Meaning
The meaning behind my "Surprise Box" project, except from making whoever receives the box surprised/happy, also symbolizes my view of protecting the environment:
During my environmental volunteering trip this semester, I was surprised by how ignorant people could be and don't think that our action can actually have influence on the environment.
And the plant/ moss part of the project conveys my idea that personally, I think plants have "hearts", or their feelings too. So when people cut a tree, it can feel the pain. The flowers on the heart and the butterfly symbolize the beauty and purity of the nature. The nature provides all these enjoyable sceneries to all the livings in this world, and they are something that we human need to treasure and protect.

I used SLS to print it. The powder I used is PA2200, which is a Nylon material, water resistant.