[css-ui-4] Fix typos

Author: frivoal

css-ui-4/Overview.bs

@@ -837,7 +837,7 @@ and are never used outside of the UA stylesheet.
 Instead, this specification only provides
 ''appearance/auto'', ''appearance/none''.
 UAs cannot therefore use the 'appearance' property
-in the UA stylesheet to give each control is native look and feel,
+in the UA stylesheet to give each control its native look and feel,
 and must use ''appearance:auto'' instead.
 
 Issue: IE supports -webkit-appearance, and also includes the textfield and button values.
@@ -864,7 +864,7 @@ so we may need to include it as well.
 On form control elements where the computed value is ''appearance/auto''
 UAs may disregard some CSS properties
 to ensure that the intended appearance is preserved,
-or because these property may not be meaningful for the chosen appearance.
+or because these properties may not be meaningful for the chosen appearance.
 However, the following properties must not be disregarded:
 <ul>
 	<li>'appearance'
@@ -897,7 +897,7 @@ must be suppressed when the appearance is changed using 'appearance',
 even if the UA's internal representation for this element
 was composed of multiple elements or pseudo elements combined together.
 For example, <{select}> is often rendered with an arrow on the right side
-indicating that the list will be expanded if the element is clicked,
+indicating that the list will be expanded if the element is clicked.
 If the computed value of 'appearance' is ''appearance/none'', this
 must disappear.