double vpr = Math.sqrt(vpw * vpw + vph * vph);
double p = value.getFloatValue(CSSPrimitiveValue.CSS_PERCENTAGE);
float val = (float)(p * vpr / 100);
ImmutableValue iv = new ImmutableFloat(CSSPrimitiveValue.CSS_NUMBER, val);
styleDeclaration.setPropertyCSSValue(getPropertyName(),
new CSSOMReadOnlyValue(iv),
priority,
origin);
} catch (IllegalStateException e) {
// Let the value unchanged.
}