I had been looking at how to do this and usually just find old .deb files but, I don't like using 5 year old .deb files that are for another version of Ubuntu.
So here is an easier way:
Code:
sudo apt update

sudo apt install git libtool pkg-config libwnck-dev libwnck-3-dev debhelper gtk3-engines-xfce libcairo2-dev libdecoration0-dev libxrender-dev libx11-dev gettext intltool intltool-debian libltdl-dev libtool autopoint automake build-essential libxi-dev

*g++-aarch64-linux-gnu --- this package may not be required to compile I leave it at your discretion whether to install it or not. 
(I left this out of the above command because I had to remove it afterwards but, it's up to you to install it if you want.)

(You may want to create a directory for these if you want, It will create 2 directories one emerald and the other emerald-themes. I created a folder in my Downloads directory called emerald that had both directories in it.)

git clone https://github.com/compiz-reloaded/emerald

git clone https://github.com/compiz-reloaded/emerald-themes

Change directories were the emerald source is, then do the following commands, the same applies for the emerald-themes directory:

./autogen.sh

*Optional step - Configure after autogen.sh is done configure with:
./configure --prefix=/usr

make

sudo make install
Here is the YouTube video I got this from: I mainly just went by the commands but, feel free to listen to the video as there is some explaining of what is going on in the video.

https://www.youtube.com/watch?v=jFlnnWqwEqg

Then go into CCSM Window decoration and put this in the command:

emerald.png