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

/* === Utility === */
.hidden {
  display: none !important;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

/* === Body === */
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: linear-gradient(135deg, #e8ecf1 0%, #f0f2f5 100%);
  display: flex;
  justify-content: center;
  padding: 60px 16px;
  color: #333;
  min-height: 100vh;
}

/* === Container === */
.container {
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.08), 0 1px 4px rgba(0, 0, 0, 0.04);
  padding: 32px;
  width: 100%;
  max-width: 500px;
}

/* === Header === */
h1 {
  text-align: center;
  margin-bottom: 24px;
  font-size: 1.6rem;
  font-weight: 700;
  color: #1a1a2e;
}

/* === Form === */
#todo-form {
  display: flex;
  gap: 8px;
  margin-bottom: 16px;
}

#todo-input {
  flex: 1;
  padding: 12px 16px;
  border: 2px solid #e0e0e0;
  border-radius: 10px;
  font-size: 1rem;
  outline: none;
  transition: border-color 0.2s, box-shadow 0.2s;
}

#todo-input:focus {
  border-color: #4a90e2;
  box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.15);
}

#todo-form button {
  padding: 12px 22px;
  background: #4a90e2;
  color: #fff;
  border: none;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s, transform 0.1s;
}

#todo-form button:hover {
  background: #357abd;
}

#todo-form button:active {
  transform: scale(0.96);
}

/* === Filters === */
.filters {
  display: flex;
  gap: 4px;
  margin-bottom: 16px;
  background: #f5f6f8;
  border-radius: 10px;
  padding: 4px;
}

.filter-btn {
  flex: 1;
  padding: 8px 12px;
  border: none;
  border-radius: 8px;
  background: transparent;
  color: #666;
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

.filter-btn:hover {
  color: #333;
}

.filter-btn.active {
  background: #fff;
  color: #4a90e2;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
  font-weight: 600;
}

/* === Todo list === */
#todo-list {
  list-style: none;
}

#todo-list li {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  border-radius: 10px;
  margin-bottom: 4px;
  transition: background 0.15s, opacity 0.3s, transform 0.3s;
}

#todo-list li:hover {
  background: #f8f9fb;
}

/* Custom checkbox */
#todo-list li .checkbox {
  appearance: none;
  -webkit-appearance: none;
  width: 20px;
  height: 20px;
  border: 2px solid #ccc;
  border-radius: 50%;
  cursor: pointer;
  transition: border-color 0.2s, background 0.2s;
  flex-shrink: 0;
  position: relative;
}

#todo-list li .checkbox:checked {
  background: #4a90e2;
  border-color: #4a90e2;
}

#todo-list li .checkbox:checked::after {
  content: "";
  position: absolute;
  top: 3px;
  left: 5.5px;
  width: 5px;
  height: 9px;
  border: solid #fff;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

#todo-list li .checkbox:focus-visible {
  outline: 2px solid #4a90e2;
  outline-offset: 2px;
}

/* Task text */
#todo-list li .text {
  flex: 1;
  font-size: 1rem;
  line-height: 1.4;
  transition: color 0.3s;
  cursor: default;
  padding: 2px 0;
}

#todo-list li.done .text {
  text-decoration: line-through;
  color: #b0b0b0;
}

/* Inline edit input */
#todo-list li .edit-input {
  flex: 1;
  font-size: 1rem;
  padding: 4px 8px;
  border: 2px solid #4a90e2;
  border-radius: 6px;
  outline: none;
  font-family: inherit;
}

/* Delete button */
#todo-list li .delete-btn {
  background: none;
  border: none;
  color: #ccc;
  font-size: 1.1rem;
  cursor: pointer;
  padding: 4px 8px;
  border-radius: 6px;
  transition: color 0.2s, background 0.2s;
  opacity: 0;
}

#todo-list li:hover .delete-btn,
#todo-list li .delete-btn:focus-visible {
  opacity: 1;
}

#todo-list li .delete-btn:hover {
  color: #e24a4a;
  background: #fdecea;
}

#todo-list li .delete-btn:focus-visible {
  outline: 2px solid #e24a4a;
  outline-offset: 2px;
}

/* === Animations === */
@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeOut {
  from {
    opacity: 1;
    transform: translateX(0);
  }
  to {
    opacity: 0;
    transform: translateX(20px);
  }
}

#todo-list li.slide-in {
  animation: slideIn 0.25s ease-out;
}

#todo-list li.fade-out {
  animation: fadeOut 0.25s ease-in forwards;
}

/* === Empty state === */
#empty-msg {
  text-align: center;
  color: #aaa;
  padding: 32px 16px;
  font-size: 0.95rem;
}

.empty-icon {
  display: block;
  font-size: 2.4rem;
  margin-bottom: 8px;
}

.empty-text {
  display: block;
}

/* === Footer === */
#todo-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 14px;
  margin-top: 8px;
  border-top: 1px solid #eee;
  font-size: 0.85rem;
  color: #999;
}

#clear-completed {
  background: none;
  border: none;
  color: #999;
  font-size: 0.85rem;
  cursor: pointer;
  padding: 4px 8px;
  border-radius: 6px;
  transition: color 0.2s, background 0.2s;
}

#clear-completed:hover {
  color: #e24a4a;
  background: #fdecea;
}

/* === Responsive === */
@media (max-width: 400px) {
  .container {
    padding: 20px 16px;
    border-radius: 12px;
  }

  #todo-form button {
    padding: 12px 14px;
  }

  .filter-btn {
    font-size: 0.8rem;
    padding: 6px 8px;
  }

  #todo-list li .delete-btn {
    opacity: 1;
  }
}