:root {
  --font-sans: 'Inter', ui-sans-serif, system-ui, sans-serif;
  --font-serif: 'Source Serif 4', ui-serif, Georgia, serif;
  --font-mono: 'JetBrains Mono', ui-monospace, 'SF Mono', Menlo, monospace;

  --color-bg: #FAFAF7;
  --color-bg-elevated: #FFFFFF;
  --color-fg: #1A1A1A;
  --color-fg-muted: #6B6864;
  --color-fg-subtle: #8A8682;
  --color-border: #E8E5DE;
  --color-border-strong: #C9C5BC;
  --color-accent: #B85450;
  --color-accent-fg: #FFFFFF;

  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
}

:root[data-theme='dark'] {
  --color-bg: #0F0F0F;
  --color-bg-elevated: #1A1A1A;
  --color-fg: #F0EFEA;
  --color-fg-muted: #8A8682;
  --color-fg-subtle: #6B6864;
  --color-border: #2A2826;
  --color-border-strong: #3A3835;
  --color-accent: #D87572;
  --color-accent-fg: #0F0F0F;
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  background: var(--color-bg);
  color: var(--color-fg);
  font-family: var(--font-sans);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  height: 100%;
}

body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  max-width: 760px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

a { color: var(--color-accent); text-underline-offset: 2px; }
a:hover { text-decoration: underline; }

::selection { background: var(--color-accent); color: var(--color-accent-fg); }

/* Header */
.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.25rem 0;
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  background: color-mix(in oklab, var(--color-bg) 90%, transparent);
  backdrop-filter: blur(8px);
  z-index: 10;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.625rem;
  text-decoration: none;
  color: var(--color-fg);
}

.brand:hover { text-decoration: none; }

.brand img { height: 28px; width: auto; }

.brand-text {
  font-weight: 600;
  letter-spacing: -0.01em;
  font-size: 1.0625rem;
}

.icon-button {
  background: transparent;
  border: 0;
  color: var(--color-fg-muted);
  cursor: pointer;
  padding: 0.5rem;
  border-radius: var(--radius-md);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 1.125rem;
  line-height: 1;
}

.icon-button:hover { color: var(--color-fg); background: var(--color-bg-elevated); }

[data-theme='light'] .theme-icon-dark,
[data-theme='dark'] .theme-icon-light { display: none; }

/* Conversation */
.conversation {
  flex: 1;
  padding: 2.5rem 0 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  min-height: 0;
  overflow-y: auto;
  scroll-behavior: smooth;
}

.welcome h1 {
  font-size: 1.875rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.15;
  margin: 0 0 0.75rem 0;
}

.welcome p {
  color: var(--color-fg-muted);
  margin: 0;
  line-height: 1.6;
}

.welcome em {
  color: var(--color-fg);
  font-style: normal;
  background: var(--color-bg-elevated);
  border: 1px solid var(--color-border);
  padding: 0.125rem 0.4rem;
  border-radius: var(--radius-md);
  font-size: 0.95em;
}

.message {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
  max-width: 100%;
  line-height: 1.65;
}

.message .role {
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--color-fg-subtle);
}

.message.user .role { color: var(--color-accent); }

.message .body {
  white-space: pre-wrap;
  word-wrap: break-word;
}

.message.assistant .body {
  font-family: var(--font-serif), var(--font-sans);
  font-size: 1.0625rem;
}

.message.error .body {
  color: var(--color-accent);
  font-style: italic;
}

.cursor {
  display: inline-block;
  width: 0.5ch;
  background: var(--color-fg);
  animation: blink 1s steps(2, start) infinite;
  margin-left: 1px;
}

@keyframes blink { to { visibility: hidden; } }

/* Composer */
.composer {
  display: flex;
  align-items: flex-end;
  gap: 0.5rem;
  padding: 0.75rem;
  margin-bottom: 0.75rem;
  background: var(--color-bg-elevated);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  position: sticky;
  bottom: 0;
}

.composer:focus-within {
  border-color: var(--color-border-strong);
}

.composer textarea {
  flex: 1;
  background: transparent;
  border: 0;
  outline: 0;
  resize: none;
  color: var(--color-fg);
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.5;
  max-height: 200px;
  padding: 0.375rem 0.25rem;
}

.composer textarea::placeholder { color: var(--color-fg-subtle); }

.composer button {
  background: var(--color-fg);
  color: var(--color-bg);
  border: 0;
  border-radius: var(--radius-md);
  width: 36px;
  height: 36px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  flex-shrink: 0;
  transition: opacity 200ms ease;
}

.composer button:hover { opacity: 0.85; }
.composer button:disabled { opacity: 0.4; cursor: not-allowed; }

.footnote {
  text-align: center;
  font-size: 0.8125rem;
  color: var(--color-fg-subtle);
  margin: 0 0 1rem 0;
}

@media (max-width: 640px) {
  body { padding: 0 1rem; }
  .welcome h1 { font-size: 1.5rem; }
  .conversation { padding-top: 1.5rem; }
}