Update mermaid styles, eg mermaidchart

[pftom]

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[jokemon]

优化建议：
调整mermaid最终渲染的样式，使其更加美观
情况描述：
目前我用refly的mermaid代码组件，能解决我不少工作中实际问题，基本都是任何设计、调整图表的需求，说清楚就能准确输出了。但是refly的mermaid渲染出图表...有点太丑了...这个看能不能改进下...我一般需要复制代码到mermaidchart中再截图

期望效果： 希望图表可渲染为适合演示或汇报的样式，最好能有几种模板可选