* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, sans-serif;
  background-color: #f2f2f2;
  color: #1f2a37;
  background: linear-gradient(to bottom, #f4f4f4, #e9ecef);
}

h1 {
  text-align: center;
  margin-top: 40px;
  margin-bottom: 30px;
  font-size: 3rem;
}

.todo-list {
  list-style: none;
  padding: 0;
  width: 80%;
  max-width: 700px;
  margin: 0 auto 40px auto;
}

.todo-list > li {
  background-color: #dce6dc;
  margin-bottom: 20px;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.08);
}

.todo-list label {
  font-size: 1.5rem;
  margin-left: 8px;
  vertical-align: middle;
}

.todo-list input[type='checkbox'] {
  vertical-align: middle;
}

.sub-item {
  margin-top: 15px;
  padding-left: 30px;
}

.sub-item li {
  margin-bottom: 8px;
}

a {
  text-decoration: none;
}

a:link {
  color: green;
}

a:visited {
  color: navy;
}

a:hover {
  color: brown;
}

a:focus {
  outline: 3px solid teal;
}

a:active {
  color: yellowgreen;
}