fix(playground): preserve layout settings when switching themes

[effie-ms]

Which Linear task is linked to this PR?

EMB-424

Why was it implemented this way?

setConfigTheme replaced the entire config.theme with the new theme preset's clone, discarding the user's layout container settings (height, maxHeight, display).

The fix destructures only the layout-related container keys from the current config before applying the new theme, then merges them back on top of the new theme's container defaults. This preserves the user's height/layout choices while letting visual container properties (borderRadius, filter, etc.) update to match the selected theme.

Visual showcase (Screenshots or Videos)

Checklist before requesting a review

• I have performed a self-review and testing of my code.
• This pull request is focused and addresses a single problem.
• If this PR modifies the Widget API or adds new features that require documentation, I have updated the documentation in the public-docs repository.

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[vinzenzLIFI]

minor find: for some reason, when i switch from default to jumper theme while having a max height set, there is a small gap at the bottom of the container. but if i switch from something else to jumper, then it looks clean only for the token container, the chain container still has the gap.

Screen.Recording.2026-06-08.at.14.58.30.mov

[vinzenzLIFI]

should we persist dark mode in local storage? it changes back to light mode after refresh (not in scope of this PR)

[effie-ms]

minor find: for some reason, when i switch from default to jumper theme while having a max height set, there is a small gap at the bottom of the container. but if i switch from something else to jumper, then it looks clean only for the token container, the chain container still has the gap.

What is happening there: the height of those long lists (e.g. tokens) is calculated dynamically (from the available space). And when we switch a theme, it is not recalculated. But the header's height seems to change because of borders.
Technically, this 2px gap is visible between a theme with the border around search input and a theme without the border. So I am thinking: if I recalculate the height on every theme switch (not to overcomplicate the parsing to find only borders) - it might not be optimal either. Restricting the header's height - also not really an option because we allow customizing the weight of borders.

I am thinking about leaving it as-is. This would be the problem only for the playground - because the integrators set the theme (borders) once and (typically) do not customize it - so they would not get affected.

[effie-ms]

should we persist dark mode in local storage? it changes back to light mode after refresh (not in scope of this PR)

Good question. To be honest, I am not sure what behaviour is more expected by users (persistence or not) 😅
On reload - it persists, on reset or switching a theme - not sure.

[vinzenzLIFI]

I agree with not overcomplicating a solution if it makes things worse.

Regarding the dark and light mode. When I set dark or light mode directly in the playground settings, it's persisted. however, when I set in the widget, it's not and will fall back to system. this is probably intended, but I wanted to mention anyway.

imho: on global reset everything should be reset back to how it was before. same should be the case for the custom theme settings. if we have a default, that must be recovered.

[github-actions]

E2E Playground results

 158 passed

Details

 158 tests across 10 suites
 1 minute, 58 seconds
 68e5d82

📥 Download full HTML report (open the run → Artifacts → playwright-report)

[effie-ms]

Regarding the dark and light mode. When I set dark or light mode directly in the playground settings, it's persisted. however, when I set in the widget, it's not and will fall back to system. this is probably intended, but I wanted to mention anyway.

I checked v3 - we indeed did not persist it when toggling the dark/light from the widget. It did apply on the DOM level, but not to the local storage.
It's possible to enable though - I have made a separate PR: #778. But I think it would be worth discussing if we want it in general, before merging.

[vinzenzLIFI]

sounds good to me. I approve this PR then and we can discuss further improvements in the new one you opened.

[tomiiide]

Looks goood!