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

:root {
  --primary-color: #4a90e2;
  --delete-color: #ff5b5b;
  --success-color: #2ecc71;
  --background-color: #f0f2f5;
  --card-background: #ffffff;
  --text-color: #2c3e50;
  --border-color: #e1e8ed;
  --input-background: #ffffff;
  --border-radius: 12px;
  --transition-speed: 0.3s;
  --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.1);
  
  --dark-background-color: #1f1f1f;
  --dark-card-background: #2d2d2d;
  --dark-text-color: #e4e4e4;
  --dark-border-color: #3a3a3a;
  --dark-input-background: #3a3a3a;
}

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  color: var(--text-color);
  background-color: var(--background-color);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding: 2rem 1rem;
}

.container {
  width: 100%;
  max-width: 800px;
  background-color: var(--card-background);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-lg);
  padding: 2rem;
  transform: translateY(0);
  animation: slideIn 0.5s ease-out;
}

.progress-container {
  background-color: #f0f0f0;
  border-radius: 10px;
  height: 8px;
  margin: 1rem 0 2rem;
  position: relative;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background-color: var(--primary-color);
  border-radius: 10px;
  transition: width 0.5s ease-in-out;
  width: 0;
}

#completion-percentage {
  position: absolute;
  right: 0;
  top: -20px;
  font-size: 0.875rem;
  color: var(--text-color);
}

.search-sort-container {
  display: flex;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.search-input {
  flex: 1;
  padding: 0.75rem 1rem;
  border: 2px solid #e1e8ed;
  border-radius: var(--border-radius);
  font-size: 0.875rem;
  transition: all var(--transition-speed);
}

.search-input:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
}

.sort-select {
  padding: 0.75rem 1rem;
  border: 2px solid #e1e8ed;
  border-radius: var(--border-radius);
  background-color: white;
  cursor: pointer;
  font-size: 0.875rem;
}

body.dark-mode {
  background-color: var(--dark-background-color);
  color: var(--dark-text-color);
}

body.dark-mode .container {
  background-color: var(--dark-card-background);
  box-shadow: var(--shadow-lg);
}

body.dark-mode input,
body.dark-mode select,
body.dark-mode button:not(.todo-delete):not([type="submit"]):not(.theme-toggle) {
  background-color: var(--dark-input-background);
  border-color: var(--dark-border-color);
  color: var(--dark-text-color);
}

body.dark-mode .todo-item {
  background-color: var(--dark-card-background);
  border-color: var(--dark-border-color);
}

body.dark-mode .todo-tag,
body.dark-mode .category-badge {
  background-color: var(--dark-border-color);
  color: var(--dark-text-color);
}

body.dark-mode .progress-container {
  background-color: #333;
}

body.dark-mode .todo-date,
body.dark-mode #completion-percentage,
body.dark-mode #items-left {
  color: #999;
}

.theme-toggle {
  background: none;
  border: none;
  color: var(--text-color);
  cursor: pointer;
  font-size: 1.5rem;
  position: absolute;
  right: 20px;
  top: 20px;
  transition: transform 0.3s ease;
  z-index: 10;
}

body.dark-mode .theme-toggle {
  color: var(--dark-text-color);
}

.theme-toggle:hover {
  transform: rotate(15deg);
}

/* Animations */
@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateX(-10px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes slideOut {
  to {
    opacity: 0;
    transform: translateX(100%);
  }
}

h1 {
  text-align: center;
  color: var(--text-color);
  margin-bottom: 2rem;
  font-size: 2.5rem;
  font-weight: 700;
  letter-spacing: -0.5px;
}

.todo-form {
  display: flex;
  gap: 1rem;
  margin-bottom: 2rem;
}

.todo-form input,
.priority-select,
.category-select {
  padding: 1rem;
  border: 2px solid #e1e8ed;
  border-radius: var(--border-radius);
  font-size: 1rem;
  transition: all var(--transition-speed);
  box-shadow: var(--shadow-sm);
}

.todo-form input {
  flex: 1;
}

.todo-form input:focus,
.priority-select:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
}

.todo-form button {
  padding: 1rem 2rem;
  background-color: var(--primary-color);
  color: white;
  border: none;
  border-radius: var(--border-radius);
  cursor: pointer;
  font-weight: 600;
  transition: all var(--transition-speed);
  box-shadow: var(--shadow-sm);
}

.todo-form button:hover {
  background-color: #357abd;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.todo-filters {
  display: flex;
  justify-content: center;
  gap: 0.75rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.todo-filters button {
  padding: 0.5rem 1.25rem;
  border: 2px solid #e1e8ed;
  background: var(--card-background);
  border-radius: var(--border-radius);
  cursor: pointer;
  font-weight: 500;
  transition: all var(--transition-speed);
}

.todo-filters button:hover {
  border-color: var(--primary-color);
  color: var(--primary-color);
}

.todo-filters button.active {
  background-color: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
}

.todo-list {
  list-style: none;
  margin-bottom: 2rem;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 1rem;
  background-color: #f8f9fa;
  border-radius: var(--border-radius);
  margin-bottom: 0.75rem;
  transition: all var(--transition-speed);
  animation: fadeIn 0.3s ease-out;
  border: 1px solid #e1e8ed;
}

.todo-item:hover {
  transform: translateX(5px);
  box-shadow: var(--shadow-sm);
}

.todo-item.completed {
  background-color: #f0f0f0;
  border-color: #e0e0e0;
}

.todo-item.completed .todo-text {
  text-decoration: line-through;
  color: #888;
}

.todo-item.slide-out {
  animation: slideOut 0.3s ease-out forwards;
}

.todo-checkbox {
  appearance: none;
  width: 20px;
  height: 20px;
  border: 2px solid #cbd5e0;
  border-radius: 6px;
  cursor: pointer;
  transition: all var(--transition-speed);
  position: relative;
  flex-shrink: 0;
}

.todo-checkbox:checked {
  background-color: var(--success-color);
  border-color: var(--success-color);
}

.todo-checkbox:checked::after {
  content: '✓';
  position: absolute;
  color: white;
  font-size: 14px;
  left: 4px;
  top: -1px;
}

.todo-content {
  flex: 1;
  display: flex;
  align-items: center;
  gap: 1rem;
}

.todo-text {
  font-size: 1rem;
  transition: color var(--transition-speed);
}

.priority-badge {
  padding: 0.25rem 0.5rem;
  border-radius: 12px;
  font-size: 0.75rem;
  color: white;
  font-weight: 500;
}

.category-badge {
  padding: 0.25rem 0.5rem;
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 500;
  background-color: #3498db;
  color: white;
  margin-left: 0.5rem;
}

.todo-date {
  font-size: 0.75rem;
  color: #666;
}

.tags-container {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.todo-tag {
  background-color: #e1e8ed;
  padding: 0.25rem 0.5rem;
  border-radius: 12px;
  font-size: 0.75rem;
  cursor: pointer;
  transition: all var(--transition-speed);
}

.todo-tag:hover {
  background-color: #d1d8dd;
}

.tag-input {
  width: 100px;
  padding: 0.25rem 0.5rem;
  border: 1px solid #e1e8ed;
  border-radius: 12px;
  font-size: 0.75rem;
}

.due-date-input {
  padding: 0.25rem 0.5rem;
  border: 1px solid #e1e8ed;
  border-radius: 12px;
  font-size: 0.75rem;
}

.todo-delete {
  padding: 0.5rem 1rem;
  background-color: transparent;
  color: var(--delete-color);
  border: 1px solid var(--delete-color);
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: all var(--transition-speed);
  font-size: 0.875rem;
  flex-shrink: 0;
}

.todo-delete:hover {
  background-color: var(--delete-color);
  color: white;
}

.todo-stats {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 1.5rem;
  border-top: 2px solid #e1e8ed;
  color: #64748b;
  font-size: 0.875rem;
}

.actions-container {
  display: flex;
  gap: 0.5rem;
}

.action-btn {
  padding: 0.5rem 1rem;
  background-color: transparent;
  color: var(--primary-color);
  border: 1px solid var(--primary-color);
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: all var(--transition-speed);
  font-size: 0.875rem;
}

.action-btn:hover {
  background-color: var(--primary-color);
  color: white;
}

#clear-completed {
  padding: 0.5rem 1rem;
  background-color: transparent;
  color: #64748b;
  border: 1px solid #64748b;
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: all var(--transition-speed);
  font-size: 0.875rem;
}

#clear-completed:hover {
  background-color: #64748b;
  color: white;
}

@media (max-width: 768px) {
  .container {
    padding: 1.5rem;
  }

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

  .todo-form button {
    width: 100%;
  }

  .todo-filters {
    gap: 0.5rem;
  }

  .todo-filters button {
    flex: 1;
    min-width: 80px;
    font-size: 0.875rem;
    padding: 0.5rem 0.75rem;
  }

  .todo-item {
    flex-direction: column;
    align-items: flex-start;
  }

  .todo-content {
    width: 100%;
    flex-wrap: wrap;
  }

  .tags-container {
    width: 100%;
    margin-top: 0.5rem;
  }

  .tag-input,
  .due-date-input {
    width: 100%;
    margin-top: 0.5rem;
  }

  .todo-delete {
    width: 100%;
    margin-top: 0.5rem;
  }
}