diff --git a/src/css/simplemde.css b/src/css/simplemde.css
index 567d801..f9687e4 100644
--- a/src/css/simplemde.css
+++ b/src/css/simplemde.css
@@ -1,4 +1,5 @@
 .CodeMirror {
+    box-sizing: border-box;
     height: auto;
     border: 1px solid #ddd;
     border-bottom-left-radius: 4px;
@@ -6,6 +7,7 @@
     padding: 10px;
     font: inherit;
     z-index: 1;
+    word-wrap: break-word;
 }
 
 .CodeMirror-fullscreen {
@@ -238,6 +240,7 @@
     display: none;
     box-sizing: border-box;
     border: 1px solid #ddd;
+    word-wrap: break-word;
 }
 
 .editor-preview-active-side {
@@ -322,4 +325,4 @@
 
 .CodeMirror .CodeMirror-placeholder {
     opacity: .5;
-}
\ No newline at end of file
+}