:root {
  --bg-color: #f0f2f5;
  --container-bg: #ffffff;
  --text-main: #333333;
  --text-sub: #555555;
  --border-color: #e0e0e0;
  --card-bg: #f8f9fa;
}

[data-theme="dark"] {
  --bg-color: #121212;
  --container-bg: #1e1e1e;
  --text-main: #f5f5f5;
  --text-sub: #a0a0a0;
  --border-color: #333333;
  --card-bg: #2a2a2a;
}

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--bg-color);
  margin: 0;
  display: flex;
  justify-content: center;
  padding-top: 50px;
  transition: background-color 0.3s ease;
}
.container {
  background: var(--container-bg);
  position: relative;
  width: 90%;
  max-width: 450px;
  padding: 30px;
  border-radius: 15px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
  transition: background 0.3s ease;
}
h1 {
  margin-top: 10px;
  color: var(--text-main);
  text-align: center;
}
p {
  text-align: center;
  font-size: 13px;
  color: var(--text-sub);
  background: var(--bg-color);
  padding: 8px;
  border-radius: 8px;
}
.theme-btn {
  position: absolute;
  top: 15px;
  left: 15px;
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 6px 10px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
}
.theme-btn:hover {
  background: var(--bg-color);
  border-color: var(--text-sub);
}
.error-banner {
  background: #ffe0e0;
  color: #e74c3c;
  padding: 10px 15px;
  border-radius: 8px;
  margin-bottom: 10px;
  font-size: 13px;
  font-weight: bold;
  display: none;
  text-align: center;
  border: 1px solid #e74c3c;
}
.error-banner.show {
  display: block;
}
input {
  width: 100%;
  padding: 12px;
  border: 2px solid #e0e0e0;
  border-radius: 8px;
  font-size: 16px;
  box-sizing: border-box;
  transition: border-color 0.3s;
}
input:focus {
  outline: none;
  border-color: #3498db;
}
.input-group {
  display: flex;
  gap: 10px;
  margin-top: 10px;
}
.input-group input {
  flex: 1;
}
.input-group button {
  padding: 10px 20px;
  background-color: #2ecc71;
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 14px;
  font-weight: bold;
  cursor: pointer;
  transition: background 0.3s;
  flex-shrink: 0;
}
.input-group button:hover {
  background-color: #27ae60;
}
#task-list {
  list-style: none;
  padding: 0;
  margin-top: 20px;
}
li {
  background: #f8f9fa;
  margin-bottom: 10px;
  padding: 12px 15px;
  border-radius: 8px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border: 1px solid #eee;
  flex-wrap: nowrap;
  gap: 8px;
  background: var(--card-bg);
  border: 1px solid var(--border-color);
}
li span.title {
  font-size: 14px;
  color: #555;
  flex: 1;
  min-width: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  color: var(--text-main);
}
li span.badge {
  font-size: 11px;
  font-weight: bold;
  padding: 3px 8px;
  border-radius: 20px;
  margin-right: 8px;
  flex-shrink: 0;
}
li button {
  background-color: #ff4757;
  color: white;
  border: none;
  padding: 6px 12px;
  border-radius: 5px;
  cursor: pointer;
  font-size: 12px;
  font-weight: bold;
  transition: background 0.3s;
  flex-shrink: 0;
}
li button:hover {
  background-color: #ff6b81;
}
li button.complete-btn {
  background-color: #2ecc71;
  margin-right: 5px;
}
li button.complete-btn:hover {
  background-color: #27ae60;
}
li button.edit-btn {
  background-color: #3498db;
  margin-right: 5px;
}
li button.edit-btn:hover {
  background-color: #2980b9;
}
.sort-buttons {
  display: flex;
  gap: 10px;
  margin-top: 10px;
}
.sort-buttons button {
  flex: 1;
  padding: 10px;
  border: none;
  border-radius: 8px;
  background-color: #3498db;
  color: white;
  font-size: 14px;
  font-weight: bold;
  cursor: pointer;
  transition: background 0.3s;
}
.sort-buttons button:hover {
  background-color: #2980b9;
}
@media (max-width: 480px) {
  .container {
    padding: 15px;
  }
  .sort-buttons {
    flex-wrap: wrap;
  }
  .sort-buttons button {
    flex: 1 1 45%;
    font-size: 12px;
    padding: 8px;
  }
  li {
    padding: 8px 10px;
    gap: 5px;
  }
  li button {
    padding: 5px 8px;
    font-size: 11px;
  }
  li span.badge {
    font-size: 10px;
    padding: 2px 6px;
  }
}