score:1

Accepted answer

if you are applying the success classname directly to the progress element, you will need the following jss:

success: {
  '-webkit-appearance'       : 'none',
  'appearance'               : 'none',
  '&::-webkit-progress-value': {
    'backgroundcolor': 'green',
  },
}

here is explained why you need to reset the appearance.

https://css-tricks.com/html5-progress-element/#article-header-id-4

score:2

in jss, pseudo-elements are prefixed with an ampersand.

'&::-webkit-progress-value': {
    background: green;
}'

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