style: Update the look and feel of the `responses` title on the API docs to make it easier to read

[SebConejo]

The structure of the API documentation is difficult to follow.

When testing an endpoint, the API documentation first displays the test response, followed by a list of possible responses. Both sections have titles, but these titles are not very prominent. They are written in small text with minimal whitespace above them, making them hard to notice. The separation between these two sections could be improved.

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My suggestions:

• [ ] Increase the white space above the title.
• [ ] If it's not enough visible, try to use a different color, or add a separator line, or even try adding emojis.

Remarks

• It looks unnecessary to increase the font size as the parent title is small too.