:root {
  --primary-color: #6366f1;
  --accent-color: #3f83f8;
  --text-color: #333333;
  --background-color: #ffffff;
  --light-gray: #f0f0f0;
  --gray: #808080;
  --dark-gray: #444;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Poppins", sans-serif;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  text-align: center;
  background: linear-gradient(
    225deg,
    rgba(64, 193, 232, 0.2),
    rgba(255, 165, 0, 0.2),
    rgba(173, 97, 130, 0.25),
    rgba(0, 200, 83, 0.2),
    rgba(64, 193, 232, 0.2),
    rgba(255, 165, 0, 0.2),
    rgba(64, 193, 232, 0.2)
  );
  background-size: 1000% 1000%;
  animation: gradientShift 6s ease infinite;
}

@keyframes gradientShift {
  0% { background-position: 0% 0%; }
  50% { background-position: 100% 0%; }
  100% { background-position: 0% 0%; }
}

.todo-container {
  background: rgba(255, 255, 255, 0.2);
  backdrop-filter: blur(10px);
  padding: 2rem;
  border-radius: 1rem;
  width: 400px;
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.15);
}

.todo-container h1 {
  font-size: 2rem;
  margin-bottom: 1.5rem;
  color: var(--text-color);
}

.input-container {
  display: flex;
  justify-content: space-between;
  margin-bottom: 1.5rem;
  gap: 0.5rem;
}

#task-input {
  flex: 1;
  padding: 0.7rem;
  border: 1px solid var(--gray);
  border-radius: 8px;
  outline: none;
  font-size: 1rem;
}

#add-task {
  background: var(--primary-color);
  color: #fff;
  border: none;
  padding: 0.7rem 1.2rem;
  border-radius: 8px;
  cursor: pointer;
  font-weight: 500;
  transition: 0.3s;
}

#add-task:hover {
  background: var(--accent-color);
}

#task-list {
  list-style: none;
  margin-top: 1rem;
  padding: 0;
}

.task-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: #ffffff90;
  padding: 0.8rem;
  margin-bottom: 0.8rem;
  border-radius: 8px;
  box-shadow: 0 3px 6px rgba(0,0,0,0.1);
  transition: 0.3s ease;
}

.task-item.completed {
  text-decoration: line-through;
  color: var(--gray);
  background: #e5e7ebc7;
}

.task-item button {
  background: var(--accent-color);
  color: white;
  border: none;
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: 0.2s;
}

.task-item button:hover {
  background: var(--primary-color);
}