Rollup merge of #83393 - GuillaumeGomez:codeblock-tooltip-position, r=Nemo157

Rollup merge of #83393 - GuillaumeGomez:codeblock-tooltip-position, r=Nemo157

Codeblock tooltip position

The codeblocks tooltips were misplaced. Normally, there is no top margin applied to a tooltip unless the codeblock is the first element of the doc block. The CSS rule was too vague though, applying it to all tooltips where the codeblock was the first child of its parent. Which can be easily seen with lists:

Before:

![Screenshot from 2021-03-22 22-05-16](https://user-images.githubusercontent.com/3050060/112059812-a667ba80-8b5c-11eb-88dd-1c598ceb3766.png)

After:

![Screenshot from 2021-03-22 22-06-31](https://user-images.githubusercontent.com/3050060/112059815-a7005100-8b5c-11eb-9e40-8fc57513e498.png)

r? ``@Nemo157``