diff --git a/dist/mermaid.css b/dist/mermaid.css
index f997400f70..ad2674b4a8 100644
--- a/dist/mermaid.css
+++ b/dist/mermaid.css
@@ -256,5 +256,5 @@ text {
 }
 
 .mermaid {
-  width:1200px;
+  width: auto;
 }
diff --git a/lib/cli.js b/lib/cli.js
index e2506e4bda..d899ee039e 100644
--- a/lib/cli.js
+++ b/lib/cli.js
@@ -109,6 +109,8 @@ cli.prototype.parse = function(argv, next) {
       } catch (err) {
         this.errors.push(err)
       }
+    } else {
+      options.css = fs.readFileSync(__dirname + '/../dist/mermaid.css')
     }
 
     this.checkPhantom = createCheckPhantom(options.phantomPath)
diff --git a/test/cli_test-parser.js b/test/cli_test-parser.js
index be03bebe1d..ab913478f5 100644
--- a/test/cli_test-parser.js
+++ b/test/cli_test-parser.js
@@ -71,6 +71,17 @@ test('setting an output directory succeeds', function(t) {
   })
 })
 
+test('not setting a css source file uses a default style', function(t) {
+  t.plan(1)
+
+  var cli = require(cliPath)
+
+  cli.parse([], function(err, msg, opt) {
+    t.ok(opt.css, 'css file is populated')
+    t.end()
+  })
+})
+
 test('setting a css source file succeeds', function(t) {
   t.plan(1)