Solid borders for custom containers

[dmohns]

Is your feature request related to a problem?

This is a suggestion to slightly change the visual styling of Custom Containers in the default theme. Currently, the Customer Containers are very simple boxes.

My suggestion would be to

• Add a faint drop shadow
• Add a solid left border with high contrast against the background

This is common way of raising text boxes in various other tools. For example Slack, WhatsApp, Signal. But also other documentation tools like Docusaurus or even Github itself.

I think this will enhance readability and gives a more polished appearance out of the box.

Describe the solution you'd like

Here is an example how it could look like.

With suggestions applied:

Currently:

Describe alternatives you've considered

Users can always customise their Custom Containers themselves to look like suggested. But changing the default theme might improve the out-of-box experience for users.

Additional context

If such a suggestion is accepted I'm more than happy to contribute the CSS changes from my example.

Validations

• Follow our Code of Conduct
• Read the docs.
• Read the Contributing Guidelines.
• Check that there isn't already an issue that asks for the same feature to avoid creating a duplicate.