# Settings UI Design — kafka

**Date:** 2026-03-22
**Status:** Approved

## Overview

A lightweight preferences popover anchored to the top-right, just below the header. Triggered by a gear icon, it lets users adjust theme, enabled engines, and search defaults without leaving their current page. All changes auto-save to `localStorage` on every interaction.

## Layout & Structure

- **Trigger**: Gear icon (⚙️) in the top-right header, aligned with the header's right edge
- **Panel**: 280px wide, max-height 420px, scrollable internally, rounded corners, subtle shadow, anchored top-right (drops down from trigger, like a dropdown)
- **Close**: × button in panel header, click outside the panel, or pressing Escape
- **No Save button** — every interaction immediately writes to `localStorage`

## Interaction Flow

1. User clicks ⚙️ → panel drops down from top-right (200ms ease)
2. User toggles/clicks → changes apply instantly to DOM + write to `localStorage`
3. User clicks × or outside or Escape → panel closes, settings persist
4. **Accessibility**: Focus is trapped within the panel while open. Trigger button uses `aria-expanded` and `aria-controls`. Escape key closes the panel.

## Mid-Search Changes

When opened during an active search on `results.html`:
- Engine toggles update `localStorage` immediately, but **current results remain unchanged**
- A subtle inline note below the engines section: *"Engine changes apply to your next search"*

## Sections

### Appearance

- Three theme buttons: ☀️ Light / 🌙 Dark / 💻 System
- Clicking immediately applies via `document.body.classList` + writes to localStorage
- "System" reads `prefers-color-scheme` and updates on change

### Engines

- 2-column grid of toggle switches for all 9 engines
- Each row: engine name + toggle switch
- Enabled = filled accent color; Disabled = gray outline

### Search Defaults

- Safe search: dropdown (Moderate / Strict / Off)
- Default format: dropdown (HTML / JSON / CSV)

## Default State

```js
const DEFAULT_PREFS = {
  theme: "system",
  engines: ["wikipedia", "arxiv", "crossref", "braveapi", "qwant", "duckduckgo", "github", "reddit", "bing"],
  safeSearch: "moderate",
  format: "html"
};
```

## Persistence

```js
// Written on every interaction
localStorage.setItem('kafka_prefs', JSON.stringify({ ... }));

// Read on page load — merge with DEFAULT_PREFS
const saved = JSON.parse(localStorage.getItem('kafka_prefs') || '{}');
const prefs = { ...DEFAULT_PREFS, ...saved };
```

## Responsive Behavior

- **Mobile (<768px)**: Panel becomes a **bottom sheet** — 100% width, slides up from the bottom, top corners rounded, max-height 70vh. Trigger moves to a fixed bottom-right FAB button.
- Panel never covers the search input

## Applied to Existing Code

- `base.html` — add gear button in header, panel markup at end of `<body>`
- `kafka.css` — popover styles, toggle switch styles, bottom sheet styles for mobile
- `settings.js` — localStorage read/write, theme application, panel toggle, aria attributes, focus trap
