@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;600&display=swap');

:root {
  --bg: linear-gradient(135deg, #0f2027, #203a43, #2c5364);
  --glass-bg: rgba(255, 255, 255, 0.1);
  --text: #fff;
  --input-bg: rgba(255, 255, 255, 0.05);
  --shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
  --border: 1px solid rgba(255, 255, 255, 0.2);
  --accent: #00c6ff;
  --accent-hover: #0077aa;
  --radius: 14px;
}

body {
  margin: 0;
  padding: 0;
  font-family: 'Inter', sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  transition: 0.3s;
}

.container {
  background: var(--glass-bg);
  backdrop-filter: blur(15px);
  box-shadow: var(--shadow);
  border: var(--border);
  padding: 40px 30px;
  border-radius: var(--radius);
  width: 90%;
  max-width: 460px;
  animation: fadeIn 0.8s ease;
}

h1 {
  text-align: center;
  margin-bottom: 25px;
  font-size: 28px;
  font-weight: 600;
}

.input-group {
  display: flex;
  margin-bottom: 20px;
}

input[type="text"] {
  flex: 1;
  padding: 12px 15px;
  border-radius: var(--radius) 0 0 var(--radius);
  border: none;
  background: var(--input-bg);
  color: var(--text);
  font-size: 16px;
  outline: none;
}

button {
  padding: 12px 18px;
  background-color: var(--accent);
  border: none;
  border-radius: 0 var(--radius) var(--radius) 0;
  color: white;
  cursor: pointer;
  font-size: 20px;
  transition: 0.25s;
}

button:hover {
  background-color: var(--accent-hover);
}

ul {
  list-style: none;
  padding: 0;
  margin-top: 20px;
  max-height: 250px;
  overflow-y: auto;
}

li {
  background: var(--input-bg);
  margin-bottom: 10px;
  padding: 12px 14px;
  border-radius: var(--radius);
  transition: background 0.2s;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 16px;
  cursor: pointer;
}

li.completed {
  text-decoration: line-through;
  opacity: 0.6;
}

li:hover {
  background: rgba(255, 255, 255, 0.15);
}

.toggle-theme {
  position: absolute;
  top: 20px;
  right: 20px;
}

.toggle-theme button {
  background: transparent;
  border: none;
  color: var(--text);
  font-size: 24px;
  cursor: pointer;
  transition: 0.3s;
}

.toggle-theme button:hover {
  color: var(--accent);
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(-20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}