Use css variable to declare sidebar's width

Author: st0012

lib/rdoc/generator/template/darkfish/css/rdoc.css

@@ -9,6 +9,10 @@
 /* vim: ft=css et sw=2 ts=2 sts=2 */
 /* Base Green is: #6C8C22 */
 
+:root {
+  --sidebar-width: 300px;
+}
+
 .hide { display: none !important; }
 
 * { padding: 0; margin: 0; }
@@ -209,7 +213,7 @@ nav {
   z-index: 10;
 
   /* Layout */
-  width: 300px;
+  width: var(--sidebar-width);
   min-height: 100vh;
   background: white;
 }
@@ -226,7 +230,7 @@ main {
 
 @media (min-width: 1024px) {
   main {
-    margin-left: 300px;
+    margin-left: var(--sidebar-width);
   }
 }