[css-shadow-parts-1] add missing )s

Author: fergald

css-shadow-parts-1/Overview.bs

@@ -111,9 +111,9 @@ They are not a rehash of the ''>>>'' combinator,
 they're simply a more convenient and consistent syntax
 for something authors can already do with <a>custom properties</a>.
 By separating out the explicitly "published" parts of an element
-(the <a>shadow part map</a>
+(the <a>shadow part map</a>)
 from the sub-parts that it merely happens to contain
-(the <a>computed shadow theme map</a>,
+(the <a>computed shadow theme map</a>),
 it also helps with encapsulation,
 as authors can use ''::part()'' without fear of accidental over-styling.