style(nodes): put styles into specific node type classes

Author: moklick

example/src/index.css

@@ -136,7 +136,7 @@ nav a.active:before {
   color: #111;
 }
 
-.dark-node {
+.react-flow__node.dark-node {
   background: #333;
   color: #f8f8f8;
 }

src/style.css

@@ -103,8 +103,6 @@
 .react-flow__node {
   position: absolute;
   color: #222;
-  font-family: sans-serif;
-  font-size: 12px;
   text-align: center;
   user-select: none;
   pointer-events: all;
@@ -131,20 +129,23 @@
   border-radius: 5px;
   width: 150px;
   background: #ff6060;
+  font-size: 12px;
 }
 
 .react-flow__node-input {
   padding: 10px;
   border-radius: 5px;
   width: 150px;
   background: #9999ff;
+  font-size: 12px;
 }
 
 .react-flow__node-output {
   padding: 10px;
   border-radius: 5px;
   width: 150px;
   background: #55dd99;
+  font-size: 12px;
 }
 
 .react-flow__handle {