1. Appearance
2. Theme Editor
3. Add the following to your style.css
4. Save

pre {
border: solid 1px #e1e1e1;
font-size: 1.2 em;
color: #404040;
margin: 10px;
padding: 10px;
background: #f2f2f2}

Now when you want to display code, add a code block to your post and then paste in your code.