The template is borrowed from NeurIPS 2021 and you can find the original files at https://neurips.cc/Conferences/2021/PaperInformation/StyleFiles.
It is recommended that you do not change the neurips_2021.sty file.
You can use the same template for the milestone and final report.
The template of poster is downloaded from ETHz Download Area. You can find the original files at https://ethz.ch/services/en/service/communication/corporate-design/download-area.html.