* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 62.5%; /* 1rem = 10px */
}

body {
    font-family: 'Poppins', 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f5f7fa;
    color: #333;
    line-height: 1.6;
    font-size: 1.6rem; /* 16px */
}

.container {
    max-width: 80rem; /* 800px */
    margin: 0 auto;
    padding: 2rem; /* 20px */
}

header {
    text-align: center;
    margin-bottom: 3rem; /* 30px */
}

header h1 {
    color: #2c3e50;
    font-size: 2.4rem; /* 24px */
    margin-bottom: 1rem; /* 10px */
}

.subtitle {
    font-size: 1.8rem; /* 18px */
    color: #34495e;
    margin-bottom: 1.5rem; /* 15px */
}

.description {
    background: #ecf0f1;
    padding: 1.5rem; /* 15px */
    border-radius: 0.8rem; /* 8px */
    font-size: 1.4rem; /* 14px */
    color: #555;
    line-height: 1.5;
}

.todo-app {
    background: white;
    border-radius: 1.2rem; /* 12px */
    box-shadow: 0 0.4rem 0.6rem rgba(0, 0, 0, 0.1); /* 0 4px 6px */
    overflow: hidden;
    margin-bottom: 3rem; /* 30px */
}

.task-section {
    background: #3498db;
    color: white;
    padding: 2.5rem; /* 25px */
    text-align: center;
}

.task-section h2 {
    margin-bottom: 2rem; /* 20px */
    font-size: 2rem; /* 20px */
}

.input-container {
    display: flex;
    gap: 1rem; /* 10px */
    max-width: 40rem; /* 400px */
    margin: 0 auto;
}

#taskInput {
    flex: 1;
    padding: 1.2rem 1.5rem; /* 12px 15px */
    border: none;
    border-radius: 2.5rem; /* 25px */
    font-size: 1.6rem; /* 16px */
    outline: none;
}

.add-btn {
    width: 4.5rem; /* 45px */
    height: 4.5rem; /* 45px */
    background: white;
    color: #3498db;
    border: none;
    border-radius: 50%;
    font-size: 2.4rem; /* 24px */
    font-weight: bold;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
}

.add-btn:hover {
    background: #2980b9;
    color: white;
    transform: scale(1.05);
}

.todo-section {
    padding: 2.5rem; /* 25px */
}

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem; /* 20px */
}

.section-header h2 {
    color: #2c3e50;
    font-size: 2rem; /* 20px */
}

.clear-btn {
    background: #e74c3c;
    color: white;
    border: none;
    padding: 0.8rem 1.6rem; /* 8px 16px */
    border-radius: 2rem; /* 20px */
    cursor: pointer;
    font-size: 1.4rem; /* 14px */
    transition: all 0.3s ease;
}

.clear-btn:hover {
    background: #c0392b;
    transform: translateY(-0.1rem); /* -1px */
}

.todo-list {
    list-style: none;
}

.todo-item {
    background: #f8f9fa;
    border: 0.1rem solid #e9ecef; /* 1px */
    border-radius: 0.8rem; /* 8px */
    padding: 1.5rem; /* 15px */
    margin-bottom: 1rem; /* 10px */
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: all 0.3s ease;
}

.todo-item:hover {
    transform: translateY(-0.2rem); /* -2px */
    box-shadow: 0 0.4rem 0.8rem rgba(0, 0, 0, 0.1); /* 0 4px 8px */
}

.todo-text {
    flex: 1;
    font-size: 1.6rem; /* 16px */
    color: #2c3e50;
}

.delete-btn {
    background: #e74c3c;
    color: white;
    border: none;
    width: 3rem; /* 30px */
    height: 3rem; /* 30px */
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.8rem; /* 18px */
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
}

.delete-btn:hover {
    background: #c0392b;
    transform: scale(1.1);
}

.empty-state {
    text-align: center;
    padding: 4rem 2rem; /* 40px 20px */
    color: #7f8c8d;
    font-style: italic;
    font-size: 1.4rem; /* 14px */
}

/* Responsive Design */

/* Small phones - 480px and below */
@media (max-width: 480px) {
    .container {
        padding: 1rem; /* 10px */
    }
    
    header h1 {
        font-size: 2rem; /* 20px */
    }
    
    .subtitle {
        font-size: 1.6rem; /* 16px */
    }
    
    .task-section {
        padding: 2rem; /* 20px */
    }
    
    .input-container {
        flex-direction: column;
        gap: 1.5rem; /* 15px */
    }
    
    .add-btn {
        width: 100%;
        height: 4rem; /* 40px */
        border-radius: 2rem; /* 20px */
    }
    
    .section-header {
        flex-direction: column;
        gap: 1.5rem; /* 15px */
        text-align: center;
    }
    
    .todo-item {
        flex-direction: column;
        gap: 1rem; /* 10px */
        text-align: center;
    }
}

/* Large phones - 481px to 768px */
@media (min-width: 481px) and (max-width: 768px) {
    .container {
        padding: 1.5rem; /* 15px */
    }
    
    .input-container {
        max-width: 100%;
    }
    
    .section-header {
        flex-direction: column;
        gap: 1.5rem; /* 15px */
        text-align: center;
    }
}

/* Tablets - 769px to 1024px */
@media (min-width: 769px) and (max-width: 1024px) {
    .container {
        max-width: 70rem; /* 700px */
    }
    
    .input-container {
        max-width: 45rem; /* 450px */
    }
}

/* Animations */
@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-1rem); /* -10px */
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.todo-item {
    animation: slideIn 0.3s ease;
}

/* Hidden class */
.hidden {
    display: none;
}