@-webkit-keyframes rules are partially removed

[prymitive]

Describe the bug

When processing a file with @-webkit-keyframes rule content of that rule gets removed, except for to statement.

To Reproduce
Steps to reproduce the behavior:

1. Have this css file:

@-webkit-keyframes shake-slow {
  2% {
    -webkit-transform: translate(7px, 8px) rotate(3.5deg);
    transform: translate(7px, 8px) rotate(3.5deg);
  }
  98% {
    -webkit-transform: translate(-4px, -6px) rotate(-2.5deg);
    transform: translate(-4px, -6px) rotate(-2.5deg);
  }
  0%,
  to {
    -webkit-transform: translate(0) rotate(0);
    transform: translate(0) rotate(0);
  }
}
@keyframes shake-slow {
  2% {
    -webkit-transform: translate(7px, 8px) rotate(3.5deg);
    transform: translate(7px, 8px) rotate(3.5deg);
  }
  98% {
    -webkit-transform: translate(-4px, -6px) rotate(-2.5deg);
    transform: translate(-4px, -6px) rotate(-2.5deg);
  }
  0%,
  to {
    -webkit-transform: translate(0) rotate(0);
    transform: translate(0) rotate(0);
  }
}

2. run purgecss purgecss --css file.css -con build/index.html --output file.css
3. Output file:

@-webkit-keyframes shake-slow {
  
  to {
    -webkit-transform: translate(0) rotate(0);
    transform: translate(0) rotate(0);
  }
}
@keyframes shake-slow {
  2% {
    -webkit-transform: translate(7px, 8px) rotate(3.5deg);
    transform: translate(7px, 8px) rotate(3.5deg);
  }
  98% {
    -webkit-transform: translate(-4px, -6px) rotate(-2.5deg);
    transform: translate(-4px, -6px) rotate(-2.5deg);
  }
  0%,
  to {
    -webkit-transform: translate(0) rotate(0);
    transform: translate(0) rotate(0);
  }
}

Config file in current dir:

module.exports = {
  content: ["build/index.html", "build/static/js/*.js", "src/**/*.{ts,tsx}"],
  css: ["build/static/css/*.css"],
  output: "build/static/css",
  variables: true,
  fontFace: false,
  keyframes: false,
  safelist: {
    greedy: [/^components-/, /^firing-[0-9]$/, /^alert-history-loading-/],
  },
};

Expected behavior

Either @-webkit-keyframes should be remove entirely or not modified at all.

Screenshots

Environment (please complete the following information):

• OS: [e.g. iOS]
• Package purgecss
• Version 4.0.3

Additional context

[AdrianBannister]

Just posting our working here for anyone interested:

const purgecss = new Purgecss({
    content: [], // content
    css: [], // css
    safelist: [/\d{1,3}%/, 'from', 'to']
})