[css-cascade-5] Fix ambiguities in wording.

Author: fantasai

css-cascade-5/Overview.bs

@@ -1516,7 +1516,7 @@ Layer Ordering</h4>
 
 	Layers that are defined inside of a [=conditional group rule=]
 	do not contribute to the layer order unless the condition is true,
-	or the [=conditional group rule=] evaluates contextually
+	or unless the [=conditional group rule=] evaluates contextually
 	for different elements on the page.
 
 	Note: A feature like "container queries"
@@ -1615,7 +1615,7 @@ Declaring Without Styles: the ''@layer'' statement at-rule</h5>
 
 	Such empty ''@layer'' rules are allowed before and after ''@import'' and ''@namespace'' rules,
 	but are not allowed between (or intermixed with) ''@import'' and ''@namespace'' rules,
-	and may not precede any ''@charset'' rule.
+	and must not precede any ''@charset'' rule.
 
 	Unlike the [[#layer-block|block syntax]],
 	multiple comma-separated layer names can be provided in this syntax,