Both meter elements should have a nested shadow box with a width specified:
| "
"
| <meter>
| max="100"
| value="70"
| <shadow:root>
| <div>
| pseudo="-webkit-meter-inner-element"
| shadow:pseudoId="-webkit-meter-inner-element"
| <div>
| pseudo="-webkit-meter-bar"
| shadow:pseudoId="-webkit-meter-bar"
| <div>
| pseudo="-webkit-meter-optimum-value"
| style="inline-size: 70%; block-size: 100%;"
| shadow:pseudoId="-webkit-meter-optimum-value"
| "
"
| <meter>
| high="6"
| low="3"
| max="10"
| min="0"
| optimum="5"
| value="10"
| <shadow:root>
| <div>
| pseudo="-webkit-meter-inner-element"
| shadow:pseudoId="-webkit-meter-inner-element"
| <div>
| pseudo="-webkit-meter-bar"
| shadow:pseudoId="-webkit-meter-bar"
| <div>
| pseudo="-webkit-meter-suboptimum-value"
| style="inline-size: 100%; block-size: 100%;"
| shadow:pseudoId="-webkit-meter-suboptimum-value"
| "
"
| <meter>
| high="6"
| low="3"
| max="10"
| min="0"
| optimum="0"
| value="10"
| <shadow:root>
| <div>
| pseudo="-webkit-meter-inner-element"
| shadow:pseudoId="-webkit-meter-inner-element"
| <div>
| pseudo="-webkit-meter-bar"
| shadow:pseudoId="-webkit-meter-bar"
| <div>
| pseudo="-webkit-meter-even-less-good-value"
| style="inline-size: 100%; block-size: 100%;"
| shadow:pseudoId="-webkit-meter-even-less-good-value"
| "
"