[css-text-3] Clarify basis of percentage text-indent. #2394

Author: fantasai

css-text-3/Overview.bs

@@ -2200,8 +2200,8 @@ Cursive Scripts</h4>
       <dt><dfn>&lt;length&gt;</dfn>
       <dd>Gives the amount of the indent as an absolute length.</dd>
       <dt><dfn>&lt;percentage&gt;</dfn>
-      <dd>Gives the amount of the indent as a percentage of the containing
-        block's logical width.
+      <dd>Gives the amount of the indent as a percentage of
+        the block container’s own <a>logical width</a>
 
         Percentages must be treated as ''0'' for the purpose of calculating [=intrinsic size contributions=],
         but are always resolved normally when performing layout.