[css-round-display] Update a device-radius property (2 values -> 1 value)

Author: hyojinLGE

css-round-display/Overview.bs

@@ -60,14 +60,14 @@ By the mechanism of media queries, if the value of the 'device-radius' media fea
 	Name: device-radius
 	Type: range
     For: @media
-	Value: [ <<length>> | <<percentage>> ]{1,2}
+	Value: [ <<length>> | <<percentage>> ]
 	Percentage: Refer to corresponding dimension of the display
 </pre>
 <p class="note">
 Note: To define a '<code>range</code>' type media feature, the feature may be written as a normal media feature, but with a '<code>min-</code>' or '<code>max-</code>' prefix on the feature name. '<code>min-</code>' or '<code>max-</code>' prefixes express 'greater or equal to' or 'smaller or equal to' constriants respectively.
 </p>
 <p>
-The two length or percentage values of the '<code>device-radius</code>' property define the radius of a quarter ellipse in terms of the shape of the corner of the outer screen edge (This is similar to the '<code>border-radius</code>' properties. see the 'border-radius' description). The first value of the '<code>device-radius</code>' property is a horizontal radius, and the second one is a vertical radius. If the second value is ommitted, it is copied from the frist. If either length is zero, the shape of screen is rectangle not rounded. Percentage value for the horizontal radius refer to the horizontal radius of the screen, whereas percentage value for the vertical radius refer to the vertical radius of the screen. Negative value is not allowed.
+The length or percentage value of the '<code>device-radius</code>' property define the radius of a quarter ellipse in terms of the shape of the corner of the outer screen edge (This is similar to the '<code>border-radius</code>' properties. see the 'border-radius' description). If the length is zero, the shape of screen is a rectangle, otherwise that is a rectangle with round corners or a regular circle. A percentage value of the '<code>device-radius</code>' is proportional to the diameter of the screen. If the screen shape is a regular circle, '<code>device-radius</code>': 50% has a true value, because a half of the diameter of the regular circle is the radius of the screen shape. An negative value is not allowed.
 </p>
 
 <div class='example'>