CSS selector for index cells
While using **Jupyter notebooks**, I like to change the **color of header cells** in Pandas dataframes (all index cells, up and left) for more **contrast between the indexes and the data itself** (especially when I'm dealing with multiple indexes after using `.groupby()` like in the picture below) :

![example](https://i.stack.imgur.com/BvvvM.png)

I used to achieve this using this CSS code :

```html
%%HTML
<style> 
.dataframe th {
background: #3f577c ;
font-family: monospace ;
color: white ;
border: 3px solid white ;
text-align: left !important ; } 
</style>
```

This worked because every index cell (in all indexes, up and left) used to be represented by a `<th> </th>` HTML tag.

However, after updating to Pandas version **`0.25.1`** from version **`0.21.x`**, the CSS stopped working because the HTML changed so only the upper index cells (column names) are wrapped in `<th> <th>` tags. The left index simply uses `<td> </td>` tags, just like the data cells (See image below. Note that both Genre and MediaTypeId are indexes):

![example](https://i.stack.imgur.com/9AeBd.jpg)

Was this intentional? I tried using `first-child` like below but it only worked with dataframes having only 2 indexes (up and left). For the dataframes with more than one index on the left, only the first index is affected :

```html
%%HTML
<style>
.dataframe th, td:first-child {
background: #3f577c ;
font-family: monospace ;
color: white ;
border: 3px solid white ;
text-align: left !important ; }                                             
</style>
```

Any ideas?