[css-color-5] Make normalization steps an ordered list

Author: LeaVerou

css-color-5/Overview.bs

@@ -120,12 +120,12 @@ in a linear-light-intensity space.
 
 Arguments are normalized as follows:
 
-- When a percentage is specified without any [=color-adjuster=]s,
+1. When a percentage is specified without any [=color-adjuster=]s,
 it is expanded to all adjusters available for the given [=colorspace=] plus alpha.
-- If the percentage is omitted and there are no adjusters present on any color arguments,
+2. If a percentage is omitted and there are no adjusters present on any color arguments,
 it defaults to 50% (an equal mix of the two colors).
-- If only some adjusters are present, the remaining ones default to 0% (i.e. the corresponding components are taken from the first color).
-- If the sum of corresponding adjusters across all colors is not 100%, percentages are scaled proportionally so that the sum is exactly 100%.
+3. If only some adjusters are present, the remaining ones default to 0% (i.e. the corresponding components are taken from the first color).
+4. If the sum of corresponding adjusters across all colors is not 100%, percentages are scaled proportionally so that the sum is exactly 100%.
 
 Issue: Do missing adjusters default to 0% everywhere, or only in the second color?
 If the former, we can end up with adjusters that sum to 0% pretty easily.