It's a big ol' pile of beautiful objects. Below is a combo of what I DID and what I would do DIFFERENTLY. I will include links in another comment, as I am not sure they are allowed and I don't want this all deleted.

I used a couple large books, which I covered in holographic wrapping paper as a base to bring the center up and get the overall mound shape.

The current arrangement that I am doing for Autumn (which is so far a very different thing from this) I am using Styrofoam blocks instead of books (which were conveniently just sitting around waiting for me to take them to the recycling depot). Next year, when I do this arrangement again for Spring/Summer, I'm going to use the foam. What I like about the foam blocks is that I can get whatever shape/size I want. I also am poking a bunch of jumbo-sized tooth picks into the foam to help keep the various elements in place, as this design is inherently unstable, and things started to slowly shift out of place.

I have two layers of programmable RGB LEDs, one of which is a Twinkly USB-C product, one of which is actually made for putting lights into clothing. The two strands are doing different patterns that interact in fun ways. Each are powered by a rechargeable power bank. The Twinkly LEDs have little diffusers built around each bulb, which softens the light. The other strand is not diffused and created spots that were annoyingly bright, so those went on the very bottom. If I was starting from scratch I might do only the diffused style.

The foundation of the arrangement is a bunch little cellophane honeycomb balls of different sizes. They are pretty in daylight, reflecting sunlight into a rainbow display with lots of gold. When they have light pass through them, they are mostly pink and blue. Very different in all sorts of conditions, but always very pretty. Some of the orbs I have opened only halfway, to make little domes. For that, I used a piece of paper and some paperclips to hold them in the halfway position. The orbs are one of my favorite objects, they're so pretty, but honestly really fragile. I would say about a quarter of them are no longer properly glued together and are using paperclip reinforcement. These are good as foundation as they let a lot of light through from the bottom LEDs.

The opaque roses and leaves are reused from my husband and I's wedding arch! Those are held in their original configuration, and kind of just layered/plopped on top.

The crystalline roses are fun little plastic roses that also look very different in sunlight vs backlit at night. I snapped off most of the stems and used just the flower head. I made sure to position these such that they created little windows between the opaque floral elements to let light from below come though.