Highlighting doesn't work in <div class="mermaid"></div>

[den-gr]

My github jekyll web site theme does not support html attributes so I can not use this syntax:

```mermaid {#class_context, align="center"}
classDiagram
class A
class B
A --> B
B --> C
```

But another syntax works:

<div id="class_context" class="mermaid">
classDiagram
class A
class B
A --> B
B --> C
</div>

However, with this syntax the extension highlighting doesn't work