The edible garden and the cottage garden go perfectly with this theme. Light colored gravel paths, especially straight ones, show up very well in the moonlight, are very easy to navigate. If the garden is designed for moonlight, it will probably also feel unified under sunlight. Many pale flowers are fragrant, so fragrance can be an underlying theme of this type of garden. The wildlife that you hope to attract to your garden form the basis for yet another theme.
Water is essential, at least a birdbath.
If your plants are intended to attract certain species, your garden will almost certainly be unified. You will still have to think about esthetics when composing the plants into a garden, but the animal's preferences will provide the unifying theme. You may have noticed how often I mention water. If your garden lacks unity, the addition of a few water features may tie it all together. A lily pond in one part of the garden, a simple fountain in another part, and a birdbath in a third part may be all that your garden needs to tie the disparate parts together.