DOC: Fix dark mode text visibility in Getting Started accordion (#60024)

[danielpintosalazar]

• closes #61377 (duplicate of #60024)

📄 Description

This pull request fixes the issue described in #61377, where the text in the accordion content of the Getting Started tutorial section was not visible in dark mode.

Although #61377 is a duplicate, the underlying problem was originally reported in #60024, and later duplicated in #60041 and #60921. This PR addresses the root cause described in those issues.

✅ Changes Made

Added CSS variables to ensure that text and background colors are consistent with the active theme:

.tutorial-card .card-header {
  --bs-card-cap-color: var(--pst-color-text-base);
  color: var(--pst-color-text-base);
  cursor: pointer;
  background-color: var(--pst-color-surface);
  border: 1px solid var(--pst-color-border);
}

.tutorial-card .card-body {
  background-color: var(--pst-color-on-background);
  color: var(--pst-color-text-base);
}

[mroeschke]

/preview

[github-actions]

Website preview of this PR available at: https://pandas.pydata.org/preview/pandas-dev/pandas/61379/

[mroeschke]

Thanks @danielpintosalazar