CSS undefined handling

css.py

from coloraide import Color as Base

class Color(Base):
    FIT = 'oklch-chroma'
    POWERLESS = True
    CARRYFORWARD = True

print('==== Case 1 ====')
color = Color.interpolate(['oklch(100% 50% 60deg)', 'oklch(50% 50% 0deg)'], space='oklch', out_space='oklch')(0.5)
Row([color.to_string(percent=True), color.convert('srgb').to_string()])

print('==== Case 2 ====')
color = Color.interpolate(['oklch(75% 0% 60deg)', 'oklch(75% 50% 0deg)'], space='oklch', out_space='oklch')(0.5)
Row([color.to_string(percent=True), color.convert('srgb').to_string()])

print('==== Case 3 ====')
color = Color.interpolate(['oklch(75% 0% none)', 'oklch(75% 50% 0deg)'], space='oklch', out_space='oklch')(0.5)
Row([color.to_string(percent=True), color.convert('srgb').to_string()])

print('==== Case 4 ====')
color = Color.interpolate(['rgb(255, 255, 255)', 'rgb(180, 6, 95)'], space='oklch', out_space='oklch')(0.5)
Row([color.to_string(percent=True), color.convert('srgb').to_string()])

print('==== Case 5 ====')
color = Color.interpolate(['oklch(75% 0% 60deg)', 'oklch(75% 50% 0deg)'], space='lch', out_space='oklch')(0.5)
Row([color.to_string(percent=True), color.convert('srgb').to_string()])