PHP Webpage / Multi File Upload / Initiate script

I need a web page written in php or other to allow 2 files to be uploaded to server. A file containing openssl.cert and the other the openssl.key. Once uploaded, a shell script on the server needs to run, using the uploaded files as inputs / command line arguments. The script is Out of Scope of this project, but needs to be able to call that script on completion of upload.

Webpage needs to be customisable via css , and responsive to size of browser launching page.