React is changing CSS in production build

1

Hello! How are you doing?
I have a problem: development react build works perfectly, but production build for some reason makes one tiny change in CSS file. It changes “opacity” from 100% to 1% in “@keyframes modal”.

.modal__inside {
  position: absolute;
  left: 25%;
  right: 25%;
  bottom: 25;
  top: 15%;
  margin: auto;
  padding: 2px;
  background-color: #ffffff;
  border: 1px solid #000000;
  z-index: 21;
  animation-name: modal;
  transform: translateY(10px);
  animation-duration: 0.3s;
  opacity: 0%;
  animation-iteration-count: 1;
  animation-fill-mode: forwards;
}
@keyframes modal {
  100% {transform: translateY(0); opacity: 1%}
}

It’s not a big deal. I’ve spent several hours to understand that everything is working fine, it’s just 1% instead of 100%. Now I can change it by hand in production build. But I want to know why it’s happening every time I make production build on this project. What did I do wrong?

My project files https://github.com/spyhere/spyhere.github.io
(opacity is edited by hand)
Thank you for your help! Cheers!