add support for CSS Values 4 viewport-relative units (#2775)

Co-authored-by: Taras Polovyi <taras.polovyi@grammarly.com>

lib/units.js

@@ -6,10 +6,18 @@
  */
 
 // units found in http://www.w3.org/TR/css3-values
+// and in https://www.w3.org/TR/css-values-4
 
 module.exports = [
     'em', 'ex', 'ch', 'rem' // relative lengths
-  , 'vw', 'vh', 'vmin', 'vmax' // relative viewport-percentage lengths
+
+  , 'vw', 'svw', 'lvw', 'dvw' // relative viewport-percentage lengths (including de-facto standard)
+  , 'vh', 'svh', 'lvh', 'dvh'
+  , 'vi', 'svi', 'lvi', 'dvi'
+  , 'vb', 'svb', 'lvb', 'dvb'
+  , 'vmin', 'svmin', 'lvmin', 'dvmin'
+  , 'vmax', 'svmax', 'lvmax', 'dvmax'
+
   , 'cm', 'mm', 'in', 'pt', 'pc', 'px' // absolute lengths
   , 'deg', 'grad', 'rad', 'turn' // angles
   , 's', 'ms' // times