Correctly trim strings for css properties

* If a unitless value is passed with a space it'll return `1 px`

src/browser/ui/dom/__tests__/CSSPropertyOperations-test.js

@@ -68,6 +68,14 @@ describe('CSSPropertyOperations', function() {
     })).toBe('left:0;margin:16px;opacity:0.5;padding:4px;');
   });
 
+  it('should trim values so `px` will be appended correctly', function() {
+    expect(CSSPropertyOperations.createMarkupForStyles({
+      margin: '16 ',
+      opacity: 0.5,
+      padding: ' 4 '
+    })).toBe('margin:16px;opacity:0.5;padding:4px;');
+  });
+
   it('should not append `px` to styles that might need a number', function() {
     var CSSProperty = require('CSSProperty');
     var unitlessProperties = Object.keys(CSSProperty.isUnitlessNumber);

src/browser/ui/dom/dangerousStyleValue.js

@@ -54,6 +54,9 @@ function dangerousStyleValue(name, value) {
     return '' + value; // cast to string
   }
 
+  if (typeof value === 'string') {
+    value = value.trim();
+  }
   return value + 'px';
 }