fix bugs

dist/css/editormd.css

@@ -2515,6 +2515,7 @@
   overflow: hidden;
   padding: 35px 0 0;
   position: relative;
+  background: #fff;
   -webkit-box-sizing: border-box;
   -moz-box-sizing: border-box;
   -ms-box-sizing: border-box;

src/scss/editormd.scss

@@ -58,7 +58,8 @@
     height: 100%;
     overflow: hidden;
     padding: 35px 0 0;
-    position: relative;
+    position: relative;   
+    background: #fff;
     @include box-sizing(border-box);
             
     textarea {