If you use download button on github, repository will not work since it is using git submodules.
To download repository with submodules use below command:
git clone --recurse-submodules https://github.com/Zergatul/cheatutils.git
To build mod by yourself go to Forge or Fabric directory and run gradlew build.
Download repo (or just /common/resources/web directory), and add JVM argument in Minecraft launcher like this:
-Dcheatutils.web.dir=C:\full\path\to\web\directory
Now local website uses static files from this directory instead of mod resources.