/* Design System Tokens */
:root {
  /* Colors */
  --color-primary-main: #E9EBDF;
  --color-primary-dark: #8B867F;
  --color-primary-light: #F5F6F0;

  --color-neutral-900: #151515;
  --color-neutral-800: #242424;
  --color-neutral-700: #3A3A3A;
  --color-neutral-600: #525252;
  --color-neutral-500: #6B6B6B;
  --color-neutral-400: #858585;
  --color-neutral-300: #A0A0A0;
  --color-neutral-200: #BCBCBC;
  --color-neutral-100: #D9D9D9;
  --color-neutral-50: #F7F7F7;
  --color-neutral-white: #FFFFFF;

  --color-border-light: rgba(233, 235, 223, 0.2);
  --color-border-default: #8B867F;

  --color-background-dark: #151515;
  --color-background-card: #242424;
  --color-background-light: #E9EBDF;
  --color-background-white: #FFFFFF;

  /* Typography */
  --font-family-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-size-xs: 12px;
  --font-size-sm: 14px;
  --font-size-base: 16px;
  --font-size-lg: 18px;
  --font-size-xl: 20px;
  --font-size-2xl: 24px;
  --font-size-3xl: 30px;
  --font-size-4xl: 36px;
  --font-size-5xl: 48px;

  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;

  /* Spacing */
  --spacing-xs: 8px;
  --spacing-sm: 12px;
  --spacing-md: 16px;
  --spacing-lg: 20px;
  --spacing-xl: 24px;
  --spacing-2xl: 32px;
  --spacing-3xl: 40px;
  --spacing-4xl: 56px;
  --spacing-5xl: 72px;

  /* Border Radius */
  --border-radius-sm: 4px;
  --border-radius-md: 8px;
  --border-radius-lg: 12px;
  --border-radius-xl: 16px;
  --border-radius-2xl: 24px;
  --border-radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

  /* Transitions */
  --transition-base: 250ms ease;
  --transition-fast: 150ms ease;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-family-sans);
  background: var(--color-neutral-white);
  min-height: 100vh;
  margin: 0;
  padding: 0;
  line-height: 1.6;
  color: var(--color-neutral-700);
}

.app-container {
  max-width: 680px;
  margin: 0 auto;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.header h1 {
  font-size: var(--font-size-5xl);
  font-weight: var(--font-weight-bold);
  color: var(--color-neutral-900);
  margin: 0 0 var(--spacing-xs) 0;
  letter-spacing: -0.02em;
}

.header .tagline {
  font-size: var(--font-size-base);
  color: var(--color-neutral-500);
  margin: 0;
}

.main-content {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.input-section {
  padding: var(--spacing-lg) var(--spacing-xl) var(--spacing-xs);
}

.task-input-container {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
}

.task-input {
  flex: 1;
  padding: var(--spacing-md) var(--spacing-lg);
  font-size: var(--font-size-base);
  font-family: var(--font-family-sans);
  border: 2px solid var(--color-neutral-200);
  border-radius: var(--border-radius-lg);
  transition: var(--transition-base);
  outline: none;
  background: var(--color-neutral-white);
  color: var(--color-neutral-900);
  height: 48px;
}

.task-input::placeholder {
  color: var(--color-neutral-400);
}

.task-input:focus {
  border-color: var(--color-primary-dark);
  box-shadow: 0 0 0 3px rgba(139, 134, 127, 0.1);
}

.add-button {
  height: 48px;
  padding: 0 var(--spacing-lg);
  background: var(--color-primary-main);
  color: var(--color-neutral-800);
  border: none;
  border-radius: var(--border-radius-lg);
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  cursor: pointer;
  transition: var(--transition-base);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  white-space: nowrap;
}

.add-button:hover {
  background: var(--color-primary-light);
}

.add-button:active {
  transform: scale(0.95);
}

.add-button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.tasks-container {
  flex: 1;
  padding: var(--spacing-xs) var(--spacing-xl) var(--spacing-xl);
  overflow-y: auto;
}

/* Task Items */
.task-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.task-item {
  margin-bottom: 2px;
  animation: slideIn 0.3s ease;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-5px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.task-content {
  display: flex;
  align-items: flex-start;
  gap: var(--spacing-sm);
  padding: var(--spacing-xs) var(--spacing-md);
  background: var(--color-neutral-white);
  border: 1px solid var(--color-neutral-200);
  border-radius: var(--border-radius-md);
  transition: var(--transition-base);
  position: relative;
  min-height: 40px;
}

.task-content:hover {
  border-color: var(--color-neutral-300);
  box-shadow: var(--shadow-sm);
}

.drag-handle {
  color: var(--color-neutral-300);
  font-size: var(--font-size-sm);
  margin-top: 2px;
  cursor: grab;
  user-select: none;
}

.task-checkbox {
  width: 18px;
  height: 18px;
  cursor: pointer;
  accent-color: var(--color-primary-dark);
  margin-top: 1px;
  flex-shrink: 0;
}

.task-text {
  flex: 1;
  font-size: var(--font-size-base);
  line-height: 1.5;
  color: var(--color-neutral-800);
  cursor: pointer;
  padding-right: var(--spacing-3xl);
}

.task-actions {
  position: absolute;
  right: var(--spacing-md);
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  gap: var(--spacing-xs);
  opacity: 0;
  transition: var(--transition-fast);
}

.task-content:hover .task-actions {
  opacity: 1;
}

.expand-button {
  padding: var(--spacing-xs);
  background: transparent;
  border: none;
  cursor: pointer;
  border-radius: var(--border-radius-sm);
  color: var(--color-neutral-400);
  font-size: var(--font-size-sm);
  transition: var(--transition-base);
}

.expand-button:hover {
  background: var(--color-neutral-100);
  color: var(--color-neutral-600);
}

.subtask-list {
  margin-top: var(--spacing-xs);
  margin-left: var(--spacing-2xl);
  position: relative;
}

.subtask-list::before {
  content: '';
  position: absolute;
  left: -12px;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--color-neutral-100);
}

.completed .task-text {
  text-decoration: line-through;
  opacity: 0.6;
  color: var(--color-neutral-500);
}

.empty-state {
  display: none;
}

.empty-state-icon {
  font-size: var(--font-size-5xl);
  margin-bottom: var(--spacing-lg);
  opacity: 0.5;
}

.empty-state h3 {
  font-size: var(--font-size-lg);
  color: var(--color-neutral-600);
  margin: 0 0 var(--spacing-sm) 0;
}

.empty-state p {
  font-size: var(--font-size-base);
  margin: 0;
}

/* Loading and Error States */
.spinner {
  display: inline-block;
  width: 16px;
  height: 16px;
  border: 2px solid var(--color-neutral-300);
  border-radius: 50%;
  border-top-color: var(--color-neutral-600);
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.error-message {
  background: var(--color-neutral-50);
  border: 1px solid var(--color-neutral-200);
  color: var(--color-neutral-700);
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--border-radius-md);
  margin-bottom: var(--spacing-md);
  font-size: var(--font-size-sm);
}

/* Brand Logo */
.brand-logo {
  text-align: center;
  padding: var(--spacing-lg) var(--spacing-xl) var(--spacing-sm);
  position: relative;
}

.brand-logo .logo-text {
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-semibold);
  color: var(--color-neutral-600);
  margin: 0;
  letter-spacing: 0.02em;
}

/* Language Switch */
.language-switch {
  position: absolute;
  top: var(--spacing-lg);
  right: var(--spacing-xl);
  z-index: 100;
}

.language-switch a {
  color: var(--color-neutral-500);
  text-decoration: none;
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--border-radius-sm);
  transition: var(--transition-base);
}

.language-switch a:hover {
  color: var(--color-neutral-700);
  background: var(--color-neutral-50);
}

/* Language Tip Banner */
.language-tip {
  background: var(--color-primary-light);
  border-bottom: 1px solid var(--color-primary-main);
  padding: var(--spacing-sm) var(--spacing-xl);
  text-align: center;
  font-size: var(--font-size-sm);
  color: var(--color-neutral-700);
  display: none;
  position: relative;
}

.language-tip a {
  color: var(--color-primary-dark);
  text-decoration: none;
  font-weight: var(--font-weight-medium);
  margin: 0 var(--spacing-xs);
}

.language-tip a:hover {
  text-decoration: underline;
}

.language-tip .close-tip {
  position: absolute;
  right: var(--spacing-md);
  top: 50%;
  transform: translateY(-50%);
  cursor: pointer;
  color: var(--color-neutral-400);
  font-weight: bold;
  padding: var(--spacing-xs);
  background: transparent;
  border: none;
  font-size: var(--font-size-lg);
  z-index: 10;
}

.language-tip .close-tip:hover {
  color: var(--color-neutral-600);
  background: rgba(0, 0, 0, 0.05);
  border-radius: var(--border-radius-sm);
}

.header {
  text-align: center;
  padding: var(--spacing-3xl) var(--spacing-xl) var(--spacing-lg);
  position: relative;
}

/* Responsive Design */
@media (max-width: 640px) {
  body {
    padding: var(--spacing-md);
  }

  .container {
    padding: var(--spacing-xl);
    margin-top: var(--spacing-lg);
  }

  .task-form {
    flex-direction: column;
  }

  .btn {
    width: 100%;
  }

  .subtasks {
    margin-left: var(--spacing-lg);
  }

  h1 {
    font-size: var(--font-size-3xl);
  }

  .language-switch {
    position: static;
    text-align: right;
    padding: var(--spacing-sm) var(--spacing-xl);
  }

  .brand-logo {
    padding: var(--spacing-md) var(--spacing-lg) var(--spacing-xs);
  }

  .brand-logo .logo-text {
    font-size: var(--font-size-base);
  }
}