No sign of install after activated

Once activated, did not show up in plugins list or Appearance. Back to add plugins where it was not indicated as installed. Clicked install and install failed because the directory already existed from previous install. Deleted directory, and same thing happened on second install.

Could be a conflict with other plugin, but I don’t have time to go through that process now.

https://www.ads-software.com/extend/plugins/imporved-simpler-css/