Add more control on card components such as background colour

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/8504

^{Originally posted by meteosimon January 30, 2024}

Description

Hi, I'm using quarto dashboard with python and I'm looking for an easy (and flexible) way to control the background color of cards. I know valueboxes and I like the way I can control their color and value using a dict. Can I control cards in a similar way?

Here's what I want my card to look like (the red one):

Generated with this input, the third column show's the way I thought would be nice to control the card? Is this somehow possible of in a similar way?

---
title: "MyDashboard"
format: dashboard
jupyter: python3
---

## Row

### Column

::: {.card title="MyTitle" expandable="false"}
Gapminder combines data from multiple sources into
unique coherent time-series that can’t be found elsewhere.
:::

### Column

<div class="card bslib-card html-fill-container bg-danger" data-title="MyTitle" data-require-bs-caller="card()">
<div class="card-header"><div class="card-title">MyTitle</div></div>
<div class="card-body html-fill-item html-fill-container bg-danger">
<p>Gapminder combines data from multiple sources into unique coherent time-series that can’t be found elsewhere.</p>
</div>
</div>

### Column

```{python}
#| content: card
#| output: false
dict(
  title = "MyTitle",
  color = "danger",
  value = """
  Gapminder combines data from multiple sources into unique coherent time-series that can’t be found elsewhere.
  """
)
```

````</div>

Start with the linked discussion and reproduce the Python dashboard from the supplied QMD example. Trace how dashboard cards and valueboxes handle attributes and background styling; done means a flexible card background-color control works in the rendered dashboard and does not disrupt existing card behavior.