Exercise 2: Two Different Inherited Properties From Two Different Ancestors — Possible Solution
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THE TEST
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    gp (id="gp") -> mid (id="mid") -> leaf (no rule)

    rule_gp  = Rule(['#gp'],  [Declaration('color', 'red')])
    rule_mid = Rule(['#mid'], [Declaration('font-weight', 'bold')])
    sheet = Stylesheet([rule_gp, rule_mid])

    compute_style_tree(gp, sheet)
    leaf.computed_style['color']
    leaf.computed_style['font-weight']

RESULT
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    leaf.computed_style['color']       -> 'red'
    leaf.computed_style['font-weight'] -> 'bold'

Both inherited values reach the leaf correctly, despite being set on
two entirely different ancestors, two levels apart from each other.

WHY BOTH VALUES ARRIVE CORRECTLY, INDEPENDENTLY
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compute_style_tree walks top-down, and at every level it builds that
element's OWN full computed_style by merging the parent's already-
computed style with its own cascade() result:

  gp:   own cascade = {'color': 'red'}
        parent_computed = None
        -> gp.computed_style = INITIAL_VALUES + {'color': 'red'}
           (font-weight stays at the initial 'normal' here)

  mid:  own cascade = {'font-weight': 'bold'}
        parent_computed = gp.computed_style (has color='red')
        -> mid.computed_style starts from INITIAL_VALUES, inherits
           color='red' from gp's computed style (color IS inheritable),
           then own.update() applies font-weight='bold' from mid's OWN
           rule
        -> mid ends up with BOTH color='red' (inherited) AND
           font-weight='bold' (its own rule) -- two properties, two
           different sources, merged into one dict

  leaf: own cascade = {} (no rule matches leaf at all)
        parent_computed = mid.computed_style (has BOTH color='red' AND
           font-weight='bold' already merged in)
        -> leaf inherits every inheritable property present in
           mid.computed_style, which by this point already includes
           mid's own inherited color as well as mid's own directly-set
           font-weight

Because each level's computed_style is a SINGLE merged dict handed
down as one unit -- not two separate "color chain" and "font-weight
chain" trackers -- inheritance for every property rides along
together in the same downward pass, regardless of which specific
ancestor originally introduced which specific property.

WHY THIS WORKS AS AN ANSWER
------------------------------
This confirms compute_style_tree's own top-down design handles the
general case, not just the single-property case shown in the chapter
body. Nothing about the algorithm has to know in advance which
properties will be set where -- every inheritable property that ends
up in ANY ancestor's computed_style, however it got there, is
automatically available to every descendant below it, because each
step only ever needs its own immediate parent's already-complete
computed_style, never the whole ancestor chain re-walked from scratch.