使用警告扩展。对于mkdocs，可以在mkdocs中配置。yml文件:

markdown_extensions:
    - admonition

然后在md文件中插入注释，如下所示:

!!! note

     This is a note.

这里有一个例子。

以下方法工作在GitHub，在GitLab…在Stackoverflow上，现在使用CommonMark!

>用Blockquote制作的一行盒子

用Blockquote制作的单行盒子

“用反划线制作的单行框”

单行盒与反刻度

' ' ' 盒子与三反tick ' ' '

Box made with Triple Backticks  

~ ~ ~ 用三个波浪线制作的盒子(删除波浪线之间的空间以使其工作) ~ ~ ~

Box made with Triple Tildes

每行开头有四个空格的方框:

    “Sometimes we must let go of our pride and do what is requested of us.”
    Padmé Amidala

．.． 还是用水平线?

三个破折号(——)组成一条水平线:

注意:“你的专注决定了你的现实。——奎刚·金。

对于更多的配置，我强烈推荐优秀的GitLab Markdown指南。 你也可以检查不太详细的GitHub基本格式语法。 您可以使用Babelmark比较Markdown实现。

有用提示:

要强制换行，在行尾放置两个空格; 要转义特殊字符，使用\。

类似于Etienne的解决方案，一个简单的表格格式很好:

| | |
|-|-|
|`NOTE` | This is something I want you to notice. It has a lot of text, and I want that text to wrap within a cell to the right of the `NOTE`, instead of under it.|

另一种选择(更强调)是将内容作为无主体表的头:

|`NOTE` | This is something I want you to notice. It has a lot of text, and I want that text to wrap within a cell to the right of the `NOTE`, instead of under it.|
|-|-|

最后，你可以添加一条水平线(主题断线)来创建一个封闭的方框(尽管线条样式与表中的标题行略有不同):

| | |
|-|-|
|`NOTE` | This is something I want you to notice. It has a lot of text, and I want that text to wrap within a cell to the right of the `NOTE`, instead of under it.|

---

注意文本后面的空行。

我通常在标记文本中放置警告框(例如，注意或警告)(不仅在使用pandoc时，而且在任何支持标记的地方)是用两条水平线围绕内容:

---
**NOTE**

It works with almost all markdown flavours (the below blank line matters).

---

大概是这样的:

NOTE

它适用于所有降价的口味(下面的空白行很重要)。

好消息是你不需要担心哪个降价风味是支持的，或者安装或启用了哪个扩展。

编辑:正如@filups21在评论中提到的，在RMarkdown中，一条水平线似乎是由***表示的。所以，之前提到的解决方案并不像最初声称的那样适用于所有廉价口味。

截至2021年9月: 这里有一种方法建立一个文本框在markdown使用html div标签和类'warning'。它在Jupyter Notebook和Typora上工作得很好。 您可以修改背景和字体颜色。

<div class="warning" style='padding:0.1em; background-color:#E9D8FD; color:#69337A'>
<span>
<p style='margin-top:1em; text-align:center'>
<b>On the importance of sentence length</b></p>
<p style='margin-left:1em;'>
This sentence has five words. Here are five more words. Five-word sentences are fine. But several together bocome monotonous. Listen to what is happening. The writing is getting boring. The sound of it drones. It's like a stuck record. The ear demands some variety.<br><br>
    Now listen. I vary the sentence length, and I create music. Music. The writing sings. It has a pleasent rhythm, a lilt, a harmony. I use short sentences. And I use sentences of medium length. And sometimes when I am certain the reader is rested, I will engage him with a sentence of considerable length, a sentence that burns with energy and builds with all the impetus of a crescendo, the roll of the drums, the crash of the cymbals -- sounds that say listen to this, it is important.
</p>
<p style='margin-bottom:1em; margin-right:1em; text-align:right; font-family:Georgia'> <b>- Gary Provost</b> <i>(100 Ways to Improve Your Writing, 1985)</i>
</p></span>
</div>

或者(在设计上增加一点——圆角和边框)

<div class="warning" style='background-color:#E9D8FD; color: #69337A; border-left: solid #805AD5 4px; border-radius: 4px; padding:0.7em;'>
<span>
<p style='margin-top:1em; text-align:center'>
<b>On the importance of sentence length</b></p>
<p style='margin-left:1em;'>
This sentence has five words. Here are five more words. Five-word sentences are fine. But several together bocome monotonous. Listen to what is happening. The writing is getting boring. The sound of it drones. It's like a stuck record. The ear demands some variety.<br><br>
    Now listen. I vary the sentence length, and I create music. Music. The writing sings. It has a pleasent rhythm, a lilt, a harmony. I use short sentences. And I use sentences of medium length. And sometimes when I am certain the reader is rested, I will engage him with a sentence of considerable length, a sentence that burns with energy and builds with all the impetus of a crescendo, the roll of the drums, the crash of the cymbals -- sounds that say listen to this, it is important.
</p>
<p style='margin-bottom:1em; margin-right:1em; text-align:right; font-family:Georgia'> <b>- Gary Provost</b> <i>(100 Ways to Improve Your Writing, 1985)</i>
</p></span>
</div>

一行

> hello
> world

你好 世界

多线

方法

> hello
> 
> world (new line)

你好 世界(新线)

方法b

> ```shell
> echo hello
> echo world
> ```

回声你好 呼应世界