You can grab the IPK from github and put it into packages/ folder of the image builder and it will be available to be included in the PACKAGES variable.
You can remove the packages by prepending them with a minus sign in the PACKAGES variable as well: PACKAGES="luci-theme-argon -luci-theme-openwrt".
Most of the themes I've had experience with activate themselves on install, not sure if argon does.
PS. You use the term pre-compile, which is what people normally use when talking about SDK, not image builder, but given the scope of your thread, I assumed you still meant Image Builder, not SDK.
that package is not in default repositories, so you need to download the package file and put it in a folder, then add that folder to repository list of image builder before you can add it
Thanks. So I created a directory called packages like /root/openwrt-imagebuilder-ramips-mt76x8.Linux-x86_64/packages
and added this on repo file like src custom file:///root/openwrt-imagebuilder-ramips-mt76x8.Linux-x86_64/packages