DOC: CSS in new doc theme truncates Series table rows.
#### Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.html

#### Documentation problem

System:
```
Windows 10         10.0.18363 Build 18363
Firefox            78.9esr (64-bit)
Chrome             89.0.4389.128 (Official Build) (64-bit)
MS Edge            89.0.774.75 (Official build) (64-bit)
Resolution:        1920x1080
```

The `main` element on the page referenced renders too narrowly. This truncates longer entries.

![image](https://user-images.githubusercontent.com/403865/114914259-52f52f00-9ddf-11eb-9ccc-666404c1264a.png)

#### Suggested fix for documentation

The definition for the `main` element is as follows:

```
<main class="col-12 col-md-9 col-xl-7 py-md-5 pl-md-5 pr-md-4 bd-content" role="main">
```

Adjusting the flex breakpoint `col-xl` to use eight columns provides enough space for the content.

```
<main class="col-12 col-md-9 col-xl-8 py-md-5 pl-md-5 pr-md-4 bd-content" role="main">
```

![image](https://user-images.githubusercontent.com/403865/114914525-a10a3280-9ddf-11eb-91a9-e4bf147dcd87.png)

It might be that an `overflow` declaration would work, but this seems straightforward and there seems to be room on the right of the page. Of course I don't know how this change would cascade.