Demo-site : Minor css and html changes

Author: robintom

src/demo/index.jsx

@@ -58,6 +58,7 @@ class Demo extends Component {
                 type="number"
                 value={numInputs}
                 onChange={this.handleChange}
+                min="0"
               />
             </label>
           </div>

src/demo/styles.css

@@ -112,6 +112,15 @@ input[type=number]::-webkit-outer-spin-button {
 
 .margin-top--small {
   margin-top: 1rem;
+  margin-bottom: -1rem;
+}
+
+.margin-top--small > div {
+  flex-wrap: wrap;
+}
+
+.margin-top--small > div > div {
+  margin-bottom: 1rem;
 }
 
 .margin-top--medium {