[css-color-hdr][editorial] better wording

Author: svgeesus

css-color-hdr-1/Overview.bs

@@ -239,7 +239,7 @@ because the darkest color also gets brighter.
 <div class="example" id="ex-SDR-brighter-dynamic-range">
 	For example, an [=sRGB=] screen, 
 	might be set so that white has a luminance of 160 cd/m²
-	so the deepest black has a luminance of 0.4 cd/m².
+	so the deepest black now has a luminance of 0.4 cd/m².
 	The dynamic range is still 8.6 stops.
 </div>