Updated selects in MD theme to correspond other inputs' style

boards/static/css/md/base_page.css

@@ -162,7 +162,7 b' p, .br {'
     vertical-align: middle;
 }
 
-.post-form input:not([name="image"]), .post-form textarea {
+.post-form input:not([name="image"]), .post-form textarea, .post-form select {
     background: #333;
     color: #fff;
     border: solid 1px;