A progress element should have a nested shadow box with a width specified:
| <progress>
| max="100"
| style="-webkit-appearance: none;"
| value="70"
| <shadow:root>
| <div>
| pseudo="-webkit-progress-inner-element"
| shadow:pseudoId="-webkit-progress-inner-element"
| <div>
| pseudo="-webkit-progress-bar"
| shadow:pseudoId="-webkit-progress-bar"
| <div>
| pseudo="-webkit-progress-value"
| style="inline-size: 70%; block-size: 100%;"
| shadow:pseudoId="-webkit-progress-value"