@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&display=swap');

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
}

:root {
    --primary: #000000;
    --primary-dark: #000000;
    --primary-light: #333333;
    --secondary: #000000;
    --success: #000000;
    --danger: #dc2626; /* Exception for clear completed */
    --warning: #000000;
    --dark: #000000;
    --light: #ffffff;
    --gray: #71717a;
    --bg-body: #ffffff;
    --bg-card: #ffffff;
    --text-primary: #000000;
    --text-secondary: #71717a;
    --border-color: #000000;
    --shadow-md: none;
    --shadow-lg: none;
    --radius: 0px;
}

@media (prefers-color-scheme: dark) {
    :root {
        --primary: #ffffff;
        --primary-dark: #ffffff;
        --primary-light: #e4e4e7;
        --light: #1a1a1a;
        --bg-body: #000000;
        --bg-card: #000000;
        --text-primary: #ffffff;
        --text-secondary: #a1a1aa;
        --border-color: #ffffff;
    }
}

html {
    scroll-behavior: smooth;
}

body {
    background: var(--bg-body);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

.container {
    width: 90%;
    max-width: 800px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Navigation */
nav {
    background: var(--bg-card);
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
    border-bottom: 1px solid var(--border-color);
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 0;
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary);
    text-decoration: none;
    letter-spacing: -0.5px;
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 8px;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    padding: 8px 16px;
    border-radius: 10px;
    transition: all 0.3s ease;
}

.nav-links a:hover {
    color: var(--primary);
}

.hamburger {
    display: none;
    width: 44px;
    height: 44px;
    background: transparent;
    border-radius: 12px;
    cursor: pointer;
    position: relative;
    z-index: 1001;
    align-items: center;
    justify-content: center;
}

.hamburger:hover {
    background: var(--primary);
    color: var(--bg-body);
}

.hamburger:hover .bar {
    background: var(--bg-body);
}

.hamburger.active .bar {
    background: var(--bg-body);
}

.hamburger .bar {
    display: block;
    width: 20px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    transition: all 0.3s ease;
}

.hamburger .bar:nth-child(1) { top: 14px; }
.hamburger .bar:nth-child(2) { top: 21px; }
.hamburger .bar:nth-child(3) { top: 28px; }

.hamburger.active .bar:nth-child(1) {
    top: 21px;
    transform: translateX(-50%) rotate(45deg);
    background: var(--primary);
}

.hamburger.active .bar:nth-child(2) {
    opacity: 0;
    transform: translateX(-50%) scaleX(0);
}

.hamburger.active .bar:nth-child(3) {
    top: 21px;
    background: var(--primary);
    transform: translateX(-50%) rotate(-45deg);
}

.nav-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.4);
    backdrop-filter: blur(4px);
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s ease;
    z-index: 998;
}

.nav-overlay.active {
    opacity: 1;
    visibility: visible;
}

/* Background Particles Canvas */
#bg-canvas {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    pointer-events: none;
}

/* Hero Section */
.hero {
    padding: 140px 0 80px;
}

.hero-card {
    background: transparent;
    text-align: center;
    padding: 40px 20px;
    border-radius: var(--radius);
    border: none;
    position: relative;
    overflow: hidden;
}

.hero-card::before {
    display: none;
}

.hero-card h1 {
    font-size: 3rem;
    margin-bottom: 20px;
    color: var(--text-primary);
    font-weight: 800;
    letter-spacing: -1.5px;
}

.hero-card p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 30px;
    max-width: 500px;
    margin-left: auto;
    margin-right: auto;
}

.hero-buttons {
    display: flex;
    gap: 15px;
    justify-content: center;
    flex-wrap: wrap;
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    background: var(--primary);
    color: var(--bg-body);
    padding: 12px 28px;
    border-radius: 0;
    text-decoration: none;
    font-weight: 600;
    border: 1px solid var(--primary);
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: 0.95rem;
}

.btn:hover {
    background: var(--bg-body);
    color: var(--primary);
}

.btn:active {
    transform: translateY(0);
}

.btn-outline {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
}

.btn-outline:hover {
    background: var(--light);
    color: var(--text-primary);
    border-color: var(--gray);
}

.btn-large {
    padding: 18px 48px;
    font-size: 1.1rem;
    border-radius: 16px;
}

/* Sections */
.section {
    padding: 60px 0;
}

.section-title {
    text-align: center;
    font-size: 2rem;
    margin-bottom: 40px;
    color: var(--text-primary);
    font-weight: 800;
    letter-spacing: -0.5px;
}

.app-card {
    background: var(--bg-card);
    border-radius: var(--radius);
    padding: 32px;
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border-color);
    position: relative;
    overflow: hidden;
}

.app-card::before {
    display: none;
}

/* To-Do List Styles */
.todo-input-group {
    display: flex;
    gap: 12px;
    margin-bottom: 25px;
}

.todo-input-group input {
    flex: 1;
    padding: 12px 16px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 0.95rem;
    background: var(--bg-card);
    color: var(--text-primary);
    outline: none;
    transition: all 0.2s;
}

.todo-input-group input:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 2px rgba(30, 27, 75, 0.05);
}

.todo-input-group input::placeholder {
    color: var(--text-secondary);
}

.todo-filters {
    display: flex;
    gap: 10px;
    margin-bottom: 25px;
    flex-wrap: wrap;
}

.filter-btn {
    padding: 8px 16px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    background: transparent;
    color: var(--text-secondary);
    cursor: pointer;
    font-weight: 500;
    transition: all 0.2s;
    font-size: 0.85rem;
}

.filter-btn:hover {
    border-color: var(--gray);
    color: var(--text-primary);
}

.filter-btn.active {
    background: var(--primary);
    border-color: var(--primary);
    color: var(--bg-body);
}

.todo-list {
    list-style: none;
    min-height: 100px;
}

.todo-item {
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 18px;
    border-bottom: 1px solid var(--border-color);
    animation: slideIn 0.3s ease;
    border-radius: 12px;
    margin-bottom: 8px;
    transition: background 0.3s;
}

.todo-item:hover {
    background: var(--primary);
    color: var(--bg-body);
}

.todo-item:hover .todo-text {
    color: var(--bg-body);
}

.todo-item:hover .todo-checkbox {
    border-color: var(--bg-body);
}

.todo-item:hover .todo-checkbox.checked {
    background: var(--bg-body);
    border-color: var(--bg-body);
}

.todo-item:hover .todo-checkbox.checked::after {
    color: var(--primary);
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.todo-checkbox {
    width: 20px;
    height: 20px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
    flex-shrink: 0;
}

.todo-checkbox:hover {
    border-color: var(--primary);
}

.todo-checkbox.checked {
    background: var(--primary);
    border-color: var(--primary);
}

.todo-checkbox.checked::after {
    content: '\f00c';
    font-family: 'Font Awesome 6 Free';
    font-weight: 900;
    color: var(--bg-body);
    font-size: 12px;
}

.todo-text {
    flex: 1;
    font-size: 1rem;
    color: var(--text-primary);
    transition: all 0.3s;
    font-weight: 500;
}

.todo-text.completed {
    text-decoration: line-through;
    color: var(--text-secondary);
}

.todo-delete {
    width: 36px;
    height: 36px;
    border: none;
    background: transparent;
    color: var(--danger);
    border: 1px solid var(--danger);
    border-radius: 10px;
    cursor: pointer;
    opacity: 0;
    transition: all 0.3s;
    display: flex;
    align-items: center;
    justify-content: center;
}

.todo-item:hover .todo-delete {
    opacity: 1;
    border-color: var(--bg-body);
    color: var(--bg-body);
}

.todo-item:hover .todo-delete:hover {
    background: var(--bg-body);
    color: var(--danger);
    transform: scale(1.1);
}

.todo-delete:hover {
    background: var(--danger);
    color: var(--light);
    transform: scale(1.1);
}

.todo-stats {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 20px;
    padding-top: 20px;
    border-top: 1px solid var(--border-color);
}

.todo-stats span {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
}

.clear-btn {
    background: transparent;
    border: none;
    color: var(--danger);
    cursor: pointer;
    font-weight: 600;
    transition: all 0.3s;
    padding: 8px 16px;
    border-radius: 8px;
}

.clear-btn:hover {
    background: rgba(239, 68, 68, 0.1);
}

.todo-empty {
    text-align: center;
    padding: 50px;
    color: var(--text-secondary);
}

.todo-empty i {
    font-size: 3rem;
    margin-bottom: 15px;
    opacity: 0.3;
}

/* Quiz App Styles */
.quiz-screen {
    text-align: center;
}

.quiz-screen.hidden {
    display: none;
}

.quiz-icon {
    font-size: 4rem;
    color: var(--primary);
    margin-bottom: 20px;
}

.quiz-info h3 {
    font-size: 1.8rem;
    margin-bottom: 12px;
    color: var(--text-primary);
    font-weight: 800;
    letter-spacing: -0.5px;
}

.quiz-info p {
    color: var(--text-secondary);
    margin-bottom: 30px;
    font-size: 1.05rem;
}

.quiz-rules {
    list-style: none;
    text-align: left;
    max-width: 360px;
    margin: 0 auto 32px;
    padding: 0;
}

.quiz-rules li {
    padding: 10px 0;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 0.95rem;
}

.quiz-rules li:not(:last-child) {
    border-bottom: none;
}

.quiz-rules i {
    color: inherit;
}

.quiz-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 32px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap;
    gap: 16px;
}

.quiz-progress {
    text-align: left;
}

.quiz-progress span {
    font-weight: 600;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.progress-bar {
    width: 220px;
    height: 10px;
    background: var(--border-color);
    border-radius: 10px;
    margin-top: 10px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--primary);
    border-radius: 10px;
    transition: width 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    width: 0%;
}

.quiz-score {
    color: var(--primary);
    padding: 8px 16px;
    border-radius: 8px;
    font-weight: 700;
    font-size: 1rem;
    border: 1px solid var(--border-color);
}

.quiz-score i {
    margin-right: 6px;
    color: var(--warning);
}

.question-container {
    margin-bottom: 30px;
}

.question-text {
    font-size: 1.35rem;
    margin-bottom: 28px;
    color: var(--text-primary);
    line-height: 1.6;
    font-weight: 600;
}

.options-container {
    display: grid;
    gap: 14px;
}

.option-btn {
    padding: 16px 20px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.95rem;
    cursor: pointer;
    text-align: left;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 14px;
    font-weight: 500;
}

.option-btn:hover:not(.disabled) {
    border-color: var(--primary);
    background: var(--light);
}

.option-btn .option-letter {
    width: 36px;
    height: 36px;
    border-radius: 10px;
    background: var(--primary);
    color: var(--bg-body);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    flex-shrink: 0;
    transition: all 0.3s;
    font-size: 0.9rem;
}

.option-btn:hover:not(.disabled) .option-letter {
    background: var(--bg-body);
    color: var(--primary);
}

.option-btn.correct {
    border-color: var(--primary);
    background: var(--primary);
    color: var(--bg-body);
    animation: pulse 0.5s ease;
}

.option-btn.correct .option-letter {
    background: var(--bg-body);
    color: var(--primary);
}

.option-btn.wrong {
    border-color: var(--primary);
    background: transparent;
    animation: shake 0.5s ease;
}

.option-btn.wrong .option-letter {
    background: var(--primary);
    color: var(--bg-body);
}

.option-btn.disabled {
    cursor: not-allowed;
    opacity: 0.6;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.02); }
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

.btn-next {
    margin-top: 25px;
}

.hidden {
    display: none;
}

/* Result Styles */
.result-content {
    padding: 30px 0;
}

.result-icon {
    font-size: 5rem;
    margin-bottom: 25px;
    animation: bounceIn 0.6s ease;
}

@keyframes bounceIn {
    0% { transform: scale(0); opacity: 0; }
    50% { transform: scale(1.2); }
    100% { transform: scale(1); opacity: 1; }
}

.result-icon.great {
    color: var(--success);
}

.result-icon.good {
    color: var(--primary);
}

.result-icon.average {
    color: var(--warning);
}

.result-icon.poor {
    color: var(--danger);
}

.result-content h3 {
    font-size: 2rem;
    margin-bottom: 12px;
    color: var(--text-primary);
    font-weight: 800;
}

.result-content > p {
    color: var(--text-secondary);
    margin-bottom: 35px;
    font-size: 1.1rem;
}

.result-stats {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 16px;
    margin-bottom: 35px;
}

.stat-item {
    background: var(--light);
    padding: 24px 12px;
    border-radius: 16px;
    text-align: center;
    border: 1px solid var(--border-color);
    transition: transform 0.3s;
}

.stat-item:hover {
    transform: translateY(-5px);
}

.stat-value {
    display: block;
    font-size: 2rem;
    font-weight: 800;
    color: var(--primary);
    margin-bottom: 6px;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* Footer */
footer {
    background: var(--bg-card);
    text-align: center;
    padding: 32px 0;
    margin-top: 48px;
    border-top: 1px solid var(--border-color);
}

footer p {
    color: var(--text-secondary);
    margin-bottom: 18px;
    font-weight: 500;
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: 15px;
}

.footer-links a {
    width: 40px;
    height: 40px;
    border-radius: 8px;
    background: transparent;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    text-decoration: none;
    transition: all 0.2s;
    border: 1px solid var(--border-color);
}

.footer-links a:hover {
    background: var(--primary);
    color: var(--bg-body);
    border-color: var(--primary);
}

/* Responsive */
@media (max-width: 768px) {
    .nav-links {
        position: fixed;
        top: 0;
        right: -100%;
        width: 280px;
        height: 100vh;
        background: var(--bg-card);
        flex-direction: column;
        padding: 80px 30px 30px;
        box-shadow: -10px 0 40px rgba(0, 0, 0, 0.15);
        transition: right 0.4s ease;
        z-index: 999;
        gap: 0;
    }

    .nav-links.active {
        right: 0;
    }

    .nav-links li {
        opacity: 0;
        transform: translateX(30px);
        transition: all 0.3s ease;
    }

    .nav-links.active li {
        opacity: 1;
        transform: translateX(0);
    }

    .nav-links.active li:nth-child(1) { transition-delay: 0.1s; }
    .nav-links.active li:nth-child(2) { transition-delay: 0.15s; }

    .nav-links a {
        display: block;
        padding: 16px 18px;
        font-size: 1rem;
        border-radius: 12px;
    }

    .hamburger {
        display: flex;
    }

    .hero-card {
        padding: 45px 25px;
    }

    .hero-card h1 {
        font-size: 1.8rem;
    }

    .app-card {
        padding: 28px 22px;
    }

    .todo-input-group {
        flex-direction: column;
    }

    .quiz-header {
        flex-direction: column;
        align-items: flex-start;
    }

    .progress-bar {
        width: 100%;
    }

    .result-stats {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .hero-card h1 {
        font-size: 1.5rem;
    }

    .section-title {
        font-size: 1.6rem;
    }

    .option-btn {
        padding: 14px 16px;
    }
}