[css-flexbox] Clarify pronouns in the abspos text.

Author: tabatkins

css-flexbox/Overview.html

@@ -753,7 +753,7 @@ <h3 class="heading settled heading" data-level=4.1 id=abspos-items><span class=s
 <p>	Its static position is calculated by first doing full flex layout without the absolutely-positioned elements,
 	then positioning each absolutely-positioned child as if it were the sole <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>
 	in the <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>,
-	assuming it was a fixed size box of its used size.
+	assuming both the element and the <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> were fixed size boxes of their used size.
 
 	<div class=example>
 		For example, by default, the static position of an absolutely positioned element aligns it to the main-start/cross-start corner,

css-flexbox/Overview.src.html

@@ -622,7 +622,7 @@ <h3 id='abspos-items'>
 	Its static position is calculated by first doing full flex layout without the absolutely-positioned elements,
 	then positioning each absolutely-positioned child as if it were the sole <a>flex item</a>
 	in the <a>flex container</a>,
-	assuming it was a fixed size box of its used size.
+	assuming both the element and the <a>flex container</a> were fixed size boxes of their used size.
 
 	<div class='example'>
 		For example, by default, the static position of an absolutely positioned element aligns it to the main-start/cross-start corner,