Inconsistent spacing when form fields are inside a details element

[gosko]

On the Mailing list archive search page some options are hidden inside a details element:

<details>
<summary>Advanced search options</summary>

<div class="field">
[...]

These options are displayed quite close together, with no space between them:

unlike the options at the top, outside the details element:

It would be good for the items inside the details element to have the same spacing as those outside it.

(Also if there is a better way to handle this form I am open to suggestions. The previous version of this page had separate pages for Basic Search and Advanced Search)