[BUG] Missing style for basic tables in markdown rendering

[smortex]

Describe the bug

When rendering tables in a markdown document e.g. in an OpenSearch Dashboards' notebook, the table does not have any CSS on top of the CSS reset, making it barely readable: all data is cluttered as there is no space between fields, making it hard to see where a column ends and the next one starts.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Observability', 'Notebook'
2. Create a Notebook
3. Add a paragraph
4. Add this sample content:

%md

Foo

| Mesure             | Avant   | Après  | Ratio |
|--------------------|---------|--------|-------|
| Backup incrémental | 3mn     | 20mn   | × 7   |
| Backup complet     | 1h      | 8h     | × 8   |
| Débit des backups  | 380kB/s | 62kB/s | ÷ 6   |

Bar

Expected behavior

Columns should be clearly separated, and there should be spacing above and bellow the table.

Screenshots

Current rendering of the above example (note the missing spacing between cells and after the table):

Adding some CSS can help, as an experiment I added this style to my browser to do some testing:

.euiText table {
  border-top: 2px solid #000;
  border-bottom: 2px solid #000;
  margin: 1em auto;
}

.euiText table th {
  border-bottom: 1px solid #000;
  text-align: left;
}

.euiText table th, .euiText table td {
  padding: 0 1em;
}

Host/Environment (please complete the following information):

• OUI Version: 1.3.0 I guess (what ships with the latest OSD)
• OSD Version (if applicable): 2.11.1
• OS: n/a
• Browser and version n/a (Firefox)