The code samples could not be showed in the page and the markdown editor is also not working well in my browser.
I'm using Chromium (Version 71.0.3578.98 (Official Build) Built on Ubuntu, running on LinuxMint 19.1 (64-bit).)
Sorry, it was my fault. I installed a font from OS X named Monaco, and it will let the
<pre><code> ... </code></pre>
structure doesn't works well. Well, the structure apply Monaco as a value to its font-family CSS attribute.
I uninstalled the Monaco font, and it works now. Sorry to disturb.