An example building using Carved Dark Oak
A special group of decorative blocks are called Carved Wood blocks. They are crafted using a Carving Bench from normal logs, or a knife from stripped logs. If using a knife, one of eight variations of that Carved Wood will be crafted depending on the relative positions of the Knife and stripped log in the crafting grid. Each variation of a Carved Wood has different visual patterns on it but they are all designed to fit together so that you can create nice looking builds.
As of version 1.15.2-2.5.7, all overworld logs have carved wood variations.
An example build using carved jungle
An example build using carved acacia
An example build using carved spruce
These are the carved wood variants for nether stems, namely Crimson Stem and Warped Stem. Differing from their overworld counterparts, these blocks have netherly animations!
Demonic radiance of carved crimson stem
Uncanny squirms of carved warped stem
You can craft a Carving Bench that will allow you to easily craft carved wood.
With the Carving Bench, you can craft carved wood as well as stripped wood very easily
You can craft Carving Bench using 4 planks and 2 knives