Restore basic element styles for modal dialog content (#2021)

## Motivation for the change, related issues

We added a general CSS reset to the web app styles in
#1759, and some
modal dialog content depended on user agent styles for rendering
properly.

For example, before the CSS reset, the GitHub auth dialog used to be
styled like this:
<img
src="https://github.com/user-attachments/assets/b3a2c91b-6a30-4385-9a90-190b510bcd44"
width="600">

After the reset, its paragraphs lost default vertical margins, and
content in a `<b>` element lost its bold look. After the reset, the
dialog looked like this:
<img
src="https://github.com/user-attachments/assets/005b8d9f-3fe2-446b-ab7f-0f9fccb47854"
width="600">

## Implementation details

The PR attempts to restore the styles assumed by modals before this
change.

This PR adds some style rules for modals to restore vertical margins to
paragraph elements and boldness to `<b>` tags. A downside to this
approach is that we'll have to manually add CSS rules every time we miss
a user agent style that was reset, but an upside to the approach is that
we can have consistent, explicit rules for the styles we require.

## Testing Instructions (or ideally a Blueprint)

Run `npm run dev`, open all the different dialogs, and confirm they are
styled as expected.

packages/playground/website/src/components/modal/style.module.css

@@ -1,6 +1,21 @@
 .modal {
 	max-width: 600px;
 
+	p {
+		margin-block: 13px;
+
+		&:first-child {
+			margin-block-start: 0;
+		}
+		&:last-child {
+			margin-block-end: 0;
+		}
+	}
+
+	b {
+		font-weight: 700;
+	}
+
 	textarea {
 		resize: vertical;
 		width: 100% !important;