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

body {
  background: #f4f4f4;
  display: flex;
  justify-content: center;
  padding: 20px;
}

.container {
  background: white;
  padding: 20px;
  border-radius: 10px;
  width: 100%;
  max-width: 500px;
  box-shadow: 0 0 10px rgba(0,0,0,0.1);
}

h1 {
  text-align: center;
  margin-bottom: 15px;
}

.task-input {
  display: flex;
  gap: 10px;
  margin-bottom: 20px;
}

.task-input input {
  flex: 1;
  padding: 10px;
}

.task-input button {
  padding: 10px;
  cursor: pointer;
}

ul {
  list-style: none;
}

li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px;
  margin-bottom: 10px;
  background: #eee;
  border-radius: 5px;
}

.completed {
  text-decoration: line-through;
  color: gray;
}

/* Mobile */
@media (max-width: 480px) {
  .task-input {
    flex-direction: column;
  }
}

/* Tablet */
@media (min-width: 481px) and (max-width: 1024px) {
  .container {
    max-width: 600px;
  }
}

/*  Desktop */
@media (min-width: 1025px) {
  .container {
    max-width: 700px;
  }
}