Merge branch 'codeblocks' into 'master'

redesign code blocks

See merge request acides/hiboo/hiboo!29

assets/app.scss

+// visible code blocks
+
+pre {
+  padding: .75rem;
+  color: #fff;
+  background: #212529;
+  border-radius: .25rem;
+}
+
+// dark theme switcher
+
 .theme-switch {
   display: inline-block;
   height: 24px;