body {
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.container {
    background-color: #fff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    width: 300px;
}

h1 {
    text-align: center;
    margin-bottom: 20px;
    font-size: 24px;
}

.add-task-btn {
    background-color: #28a745;
    color: #fff;
    border: none;
    padding: 10px;
    border-radius: 5px;
    cursor: pointer;
    width: 100%;
    font-size: 16px;
}

.add-task-btn:hover {
    background-color: #218838;
}

.task-list {
    margin-top: 20px;
}

.task-item {
    background-color: #f8f9fa;
    padding: 10px;
    margin-bottom: 10px;
    border-radius: 5px;
    display: flex;
    flex-direction: column;
}

.task-item .task-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.task-item button {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 18px;
}

.task-item button.complete {
    color: #28a745;
}

.task-item button.add-subtask {
    color: #007bff;
}

.subtask-list {
    margin-top: 10px;
    padding-left: 20px;
}

.subtask-item {
    background-color: #e9ecef;
    padding: 5px;
    margin-bottom: 5px;
    border-radius: 3px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}