[css2][editorial] fix markup

Author: tabatkins

css2/Overview.bs

@@ -8754,8 +8754,8 @@ elements is:</p>
 
   <blockquote>
     <p>'left' + 'margin-left' + 'border-left-width' + 'padding-left' + 'width'
-\+ 'padding-right' + 'border-right-width' + 'margin-right' + 'right' = width
- of containing block </p>
+      + 'padding-right' + 'border-right-width' + 'margin-right' + 'right' = width
+      of containing block </p>
   </blockquote>
 
 <p>If all three of 'left', 'width', and 'right' are <css>auto</css>: First set