/* --- Animations --- */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes pulseGlow {
    0%, 100% { box-shadow: 0 0 0 0 rgba(239, 68, 68, 0.4); }
    50% { box-shadow: 0 0 0 10px rgba(239, 68, 68, 0); }
}

@keyframes float {
    0% { transform: translate(0px, 0px) scale(1); }
    33% { transform: translate(30px, -50px) scale(1.1); }
    66% { transform: translate(-20px, 20px) scale(0.9); }
    100% { transform: translate(0px, 0px) scale(1); }
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

@keyframes flashGreen {
    0%, 100% { box-shadow: inset 0 1px 1px rgba(255,255,255,0.1), var(--shadow-main); border-color: var(--border-color); }
    50% { box-shadow: inset 0 0 40px rgba(16, 185, 129, 0.4), var(--shadow-main); border-color: var(--success-color); }
}

@keyframes shakeRed {
    0%, 100% { transform: translateX(0); box-shadow: inset 0 1px 1px rgba(255,255,255,0.1), var(--shadow-main); border-color: var(--border-color); }
    20%, 60% { transform: translateX(-8px); box-shadow: inset 0 0 40px rgba(239, 68, 68, 0.4), var(--shadow-main); border-color: var(--error-color); }
    40%, 80% { transform: translateX(8px); }
}

@keyframes confettiFall {
    0% { transform: translateY(-10vh) rotate(0deg); opacity: 1; }
    100% { transform: translateY(100vh) rotate(720deg); opacity: 0; }
}

/* --- Base & Variables --- */
:root {
    /* Professional Dark Theme Palette */
    --primary-color: #8b5cf6; /* Violet 500 */
    --primary-dark: #7c3aed; /* Violet 600 */
    --accent-color: #06b6d4; /* Cyan 500 */
    --background-color: #0f172a; /* Slate 900 */
    --glass-bg: rgba(30, 41, 59, 0.65); /* Slate 800 */
    --surface-color: rgba(15, 23, 42, 0.5); /* Deep Surface */
    --text-primary: #f8fafc; /* Slate 50 */
    --text-secondary: #94a3b8; /* Slate 400 */
    --success-color: #10b981; /* Emerald 500 */
    --error-color: #ef4444; /* Red 500 */
    --border-color: rgba(255, 255, 255, 0.08);
    --shadow-main: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    --glow-primary: 0 0 20px rgba(139, 92, 246, 0.4);
}

body.light-mode {
    /* Professional Light Theme Palette */
    --primary-color: #6366f1; /* Indigo 500 */
    --primary-dark: #4f46e5; /* Indigo 600 */
    --accent-color: #0ea5e9; /* Sky 500 */
    --background-color: #f1f5f9; /* Slate 100 */
    --glass-bg: rgba(255, 255, 255, 0.7);
    --surface-color: rgba(255, 255, 255, 0.9);
    --text-primary: #0f172a; /* Slate 900 */
    --text-secondary: #64748b; /* Slate 500 */
    --border-color: rgba(0, 0, 0, 0.08);
    --shadow-main: 0 20px 40px -10px rgba(0, 0, 0, 0.08);
    --glow-primary: 0 0 20px rgba(99, 102, 241, 0.2);
}

/* Reset margins and set a clean base font */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Poppins', sans-serif;
}

/* --- Custom Scrollbar --- */
::-webkit-scrollbar {
    width: 10px;
}

::-webkit-scrollbar-track {
    background: var(--background-color);
}

::-webkit-scrollbar-thumb {
    background: var(--surface-color);
    border-radius: 5px;
    border: 1px solid var(--border-color);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--primary-color);
}

/* Prevent mobile browser horizontal bouncing */
html {
    overflow-x: hidden;
    width: 100vw;
}

body {
    background-color: var(--background-color);
    color: var(--text-primary);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
    transition: background-color 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    overflow-x: hidden;
    position: relative;
}

/* Ambient Mesh Background */
.ambient-orb {
    position: absolute;
    border-radius: 50%;
    filter: blur(80px);
    opacity: 0.5;
    z-index: -1;
    animation: float 20s infinite cubic-bezier(0.4, 0, 0.2, 1);
}

.orb-1 {
    width: 400px;
    height: 400px;
    background: var(--primary-color);
    top: -100px;
    left: -100px;
}

.orb-2 {
    width: 300px;
    height: 300px;
    background: var(--accent-color);
    bottom: -50px;
    right: -50px;
    animation-delay: -10s;
}

/* Main application card */
.app-container {
    background: var(--glass-bg);
    backdrop-filter: blur(24px) saturate(150%);
    -webkit-backdrop-filter: blur(24px) saturate(150%);
    width: 100%;
    max-width: 700px;
    max-width: 850px;
    border-radius: 16px;
    box-shadow: inset 0 1px 1px rgba(255, 255, 255, 0.1), var(--shadow-main);
    padding: 30px;
    border: 1px solid var(--border-color);
    animation: fadeInUp 0.8s cubic-bezier(0.16, 1, 0.3, 1) forwards;
    transition: background 0.6s ease, border 0.6s ease, box-shadow 0.6s ease;
}

.screen-flash-correct {
    animation: flashGreen 0.5s ease-out;
}

.screen-shake-incorrect {
    animation: shakeRed 0.5s ease-in-out;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 15px;
    margin-bottom: 20px;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 15px;
}

.app-logo {
    width: 40px;
    height: auto;
    filter: drop-shadow(0 0 8px rgba(139, 92, 246, 0.4)); /* Glow effect */
    transition: transform 0.4s cubic-bezier(0.34, 1.56, 0.64, 1), filter 0.4s ease;
    border-radius: 10px;
}

.app-logo:hover {
    transform: scale(1.15) rotate(-5deg);
    filter: drop-shadow(0 0 15px var(--primary-color));
}

.header-right {
    display: flex;
    align-items: center;
    gap: 20px;
}

#quiz-header-info {
    display: flex;
    align-items: center;
    gap: 20px;
}

.user-info {
    font-size: 0.9rem;
    color: var(--text-secondary);
    font-weight: 500;
    display: none; /* Shown via JS */
}

@media (max-width: 600px) {
    .user-info { display: none !important; } /* Hide on small screens to save space */
}

h1 {
    color: var(--text-primary);
    font-size: 1.5rem;
    letter-spacing: -0.5px;
}

#progress-container {
    /* This is now part of a flex container, no need for its own display property */
    /* display: flex; */
    display: flex;
    flex-direction: column;
    align-items: flex-end;
}

#progress-text {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    margin-bottom: 5px;
}

.progress-bar {
    width: 120px;
    height: 6px;
    background-color: var(--surface-color);
    border-radius: 10px;
    overflow: hidden;
    border: 1px solid var(--border-color);
}

#progress-fill {
    height: 100%;
    background-color: var(--primary-color);
    width: 0%;
    transition: width 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

#question-text {
    color: var(--text-primary);
    font-size: 1.2rem;
    font-size: 1.35rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 20px;
    line-height: 1.5;
}

#question-image {
    max-width: 100%;
    max-height: 250px;
    max-height: 280px;
    border-radius: 8px;
    margin-bottom: 20px;
    margin: 0 auto 25px auto;
    display: block;
    object-fit: contain;
    box-shadow: var(--shadow-main);
}

#options-container {
    display: flex;
    flex-direction: column;
    gap: 10px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 16px;
    margin-top: 20px;
}

.option-btn {
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 15px 20px;
    font-size: 1.05rem;
    color: var(--text-primary);
    cursor: pointer;
    text-align: left;
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 65px;
    line-height: 1.4;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.option-btn:hover {
    background-color: var(--background-color);
    box-shadow: var(--glow-primary);
    border-color: var(--primary-dark);
    transform: translateY(-2px);
}

/* --- Advanced Quiz Styles --- */
.option-btn.correct {
    background-color: rgba(16, 185, 129, 0.15) !important;
    color: var(--success-color) !important;
    border-color: var(--success-color) !important;
    box-shadow: 0 0 15px rgba(16, 185, 129, 0.2);
}

.option-btn.incorrect {
    background-color: rgba(239, 68, 68, 0.15) !important;
    color: var(--error-color) !important;
    border-color: var(--error-color) !important;
}

.options-disabled {
    pointer-events: none;
}

/* --- Config & Result Area Styles --- */
#config-area {
    text-align: center;
    animation: fadeInUp 0.5s ease-out;
}

#config-area h2, #result-area h3 {
    margin-bottom: 10px;
    color: var(--text-primary);
    font-weight: 600;
}

#config-area p {
    color: var(--text-secondary);
    margin-bottom: 25px;
}

#high-score-area {
    background-color: var(--surface-color);
    padding: 8px 12px;
    border-radius: 8px;
    margin-bottom: 15px;
    font-size: 0.9rem;
    display: inline-block;
    border: 1px solid var(--border-color);
}
/* Utility class to hide elements */
.hidden {
    display: none !important;
}

#result-area {
    text-align: center;
    animation: fadeInUp 0.5s ease-out;
}

#score-text {
    font-size: 1.2rem;
    color: var(--text-secondary);
    margin: 15px 0 25px 0;
    line-height: 1.5;
}

.config-group {
    margin: 20px 0;
    text-align: left;
}

.config-group label {
    display: block;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

#level-selection label {
    display: inline-block;
    margin: 0 5px;
    cursor: pointer;
    padding: 8px 16px;
    border-radius: 20px; 
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    font-size: 0.9rem;
}

#level-selection input[type="radio"] {
    display: none;
}

#level-selection input[type="radio"]:checked + label {
    background-color: var(--primary-color);
    color: #fff;
    border-color: var(--primary-dark);
    box-shadow: var(--glow-primary);
}

#question-count,
#category-selection,
#game-mode {
    width: 100%;
    padding: 14px 45px 14px 18px;
    border-radius: 12px;
    border: 2px solid var(--border-color);
    font-size: 1rem;
    font-weight: 500;
    background-color: var(--surface-color);
    color: var(--text-primary);
    outline: none;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    appearance: none; /* Make select fields look modern */
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 16px center;
    background-size: 20px;
}

#question-count:hover,
#category-selection:hover,
#game-mode:hover {
    border-color: var(--text-secondary);
    background-color: var(--background-color);
}

#question-count:focus,
#category-selection:focus,
#game-mode:focus {
    border-color: var(--primary-color);
    background-color: rgba(139, 92, 246, 0.05); /* Slight primary tint */
    box-shadow: var(--glow-primary);
}

/* --- Advanced Auth Styles --- */
.auth-box {
    max-width: 450px;
    padding: 40px 30px;
}

.auth-header {
    text-align: center;
    margin-bottom: 30px;
}

.auth-logo {
    width: 80px;
    height: auto;
    margin-bottom: 15px;
    filter: drop-shadow(0 0 15px rgba(139, 92, 246, 0.4));
    transition: transform 0.5s cubic-bezier(0.34, 1.56, 0.64, 1), filter 0.5s ease;
    border-radius: 16px;
}

.auth-logo:hover {
    transform: scale(1.08) translateY(-5px);
    filter: drop-shadow(0 8px 25px var(--primary-color));
}

.auth-header h1 {
    font-size: 2.2rem;
    margin-bottom: 5px;
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--text-secondary) 100%);
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    letter-spacing: -0.5px;
}

.auth-header p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.input-group {
    position: relative;
    margin-bottom: 20px;
}

.auth-input {
    width: 100%;
    padding: 22px 45px 10px 15px;
    border-radius: 12px;
    border: 1px solid var(--border-color);
    background-color: var(--surface-color);
    color: var(--text-primary);
    font-size: 1rem;
    outline: none;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.auth-input:focus {
    border-color: var(--primary-color);
    background-color: rgba(139, 92, 246, 0.05); /* Slight tint */
    box-shadow: 0 0 0 4px rgba(139, 92, 246, 0.15);
}

.light-mode .auth-input:focus {
    box-shadow: 0 0 0 4px rgba(0, 188, 212, 0.15);
}

.input-group label {
    position: absolute;
    top: 50%;
    left: 15px;
    transform: translateY(-50%);
    color: var(--text-secondary);
    font-size: 1rem;
    pointer-events: none;
    transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

.auth-input:focus + label,
.auth-input:not(:placeholder-shown) + label {
    top: 12px;
    font-size: 0.75rem;
    color: var(--primary-color);
    font-weight: 600;
}

.password-toggle {
    position: absolute;
    right: 15px;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: color 0.3s ease;
}

.password-toggle:hover {
    color: var(--primary-color);
}

.password-toggle svg {
    width: 20px;
    height: 20px;
}

.forgot-password-container {
    text-align: right;
    margin-top: -10px;
    margin-bottom: 15px;
}

.forgot-password {
    font-size: 0.85rem;
    color: var(--primary-color);
    text-decoration: none;
    transition: opacity 0.3s ease;
}

.forgot-password:hover {
    text-decoration: underline;
}

.spinner {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid currentColor;
    border-bottom-color: transparent;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    vertical-align: middle;
    margin-right: 8px;
}

/* --- Terms and Conditions Styles --- */
.tnc-content {
    max-height: 180px;
    overflow-y: auto;
    background-color: rgba(0, 0, 0, 0.05);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    padding: 15px;
    margin-bottom: 20px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-align: left;
}

.tnc-content ul {
    margin-top: 10px;
    margin-bottom: 10px;
    padding-left: 20px;
}

.tnc-content li {
    margin-bottom: 6px;
}

.light-mode .tnc-content {
    background-color: rgba(255, 255, 255, 0.5);
}

.tnc-checkbox-group {
    display: flex;
    align-items: flex-start;
    gap: 12px;
    margin-bottom: 20px;
    text-align: left;
}

.tnc-checkbox-group input {
    width: 18px;
    height: 18px;
    accent-color: var(--primary-color);
    cursor: pointer;
    margin-top: 2px;
}

.tnc-checkbox-group label {
    font-size: 0.9rem;
    color: var(--text-primary);
    cursor: pointer;
    line-height: 1.4;
}

.auth-submit {
    width: 100%;
    padding: 14px;
    font-size: 1.1rem;
    margin-top: 10px;
    box-shadow: var(--shadow-main);
}

.primary-btn:disabled, 
.auth-submit:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.auth-divider {
    display: flex;
    align-items: center;
    text-align: center;
    margin: 25px 0;
    color: var(--text-secondary);
}

.auth-divider::before,
.auth-divider::after {
    content: '';
    flex: 1;
    border-bottom: 1px solid var(--border-color);
}

.auth-divider span {
    padding: 0 15px;
    font-size: 0.9rem;
    font-weight: 600;
}

.google-btn {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 10px;
    background-color: transparent;
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    padding: 12px 20px;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    width: 100%;
}

.google-btn:hover {
    background-color: var(--surface-color);
    border-color: var(--primary-color);
    transform: translateY(-2px);
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.1);
}

.google-icon {
    width: 20px;
    height: 20px;
}

.auth-switch {
    text-align: center;
    margin-top: 25px;
    font-size: 0.95rem;
    color: var(--text-secondary);
}

.auth-switch a {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 600;
    margin-left: 5px;
    transition: color 0.3s ease;
}

.auth-switch a:hover {
    opacity: 0.8;
}

.auth-message {
    text-align: center;
    margin-top: 15px;
    font-size: 0.9rem;
    min-height: 20px;
    color: var(--error-color);
}

#iq-score-container {
    margin: 20px 0;
    padding: 20px;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    border-radius: 16px;
    color: #fff;
    box-shadow: var(--glow-primary);
}

#iq-score-label {
    display: block;
    font-size: 1rem;
    color: rgba(255, 255, 255, 0.7);
}

#iq-score-value {
    display: block;
    font-size: 4rem;
    font-weight: bold;
    color: #fff;
    text-shadow: 0 4px 20px rgba(0,0,0,0.3);
}

#results-graph-container {
    display: flex;
    gap: 2px;
    height: 50px;
    margin-bottom: 20px;
}

.result-bar {
    flex-grow: 1;
    background-color: var(--border-color); /* Default/skipped color */
    border-radius: 2px;
}

.primary-btn {
    background: linear-gradient(45deg, var(--accent-color), var(--primary-color)); /* Use accent for start */
    color: var(--text-primary);
    border: none;
    padding: 12px 24px;
    border-radius: 5px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    margin-top: 10px;
}

.primary-btn:hover {
    background: linear-gradient(45deg, var(--primary-dark), var(--primary-color)); /* Darker primary on hover */
    transform: translateY(-2px);
    box-shadow: 0 4px 20px rgba(0,0,0,0.3);
}

.result-bar.correct {
    background-color: var(--success-color);
}

.result-bar.incorrect {
    background-color: var(--error-color);
}

#explanations-container {
    margin-top: 30px;
    margin-bottom: 25px;
    text-align: left;
    animation: fadeInUp 0.6s ease-out;
}

#explanations-container h3 {
    margin-bottom: 15px;
    text-align: center;
    font-size: 1.1rem;
}

.explanation-card {
    background-color: var(--surface-color);
    border-left: 4px solid var(--error-color);
    padding: 15px;
    margin-bottom: 15px;
    border-radius: 0 12px 12px 0;
    box-shadow: var(--shadow-main);
}

.explanation-card p {
    margin-bottom: 5px !important;
    font-size: 0.95rem;
}

.explanation-card .exp-text {
    color: var(--text-secondary) !important;
    margin-top: 10px !important;
}

#timer-container {
    display: flex;
    justify-content: center;
    align-items: center;
    min-width: 40px;
    padding: 0 10px;
    height: 40px;
    border-radius: 20px; /* Pill shape to accommodate longer text */
    border: 2px solid var(--primary-color);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

#timer-container.timer-low {
    border-color: var(--error-color);
    animation: pulseGlow 1s infinite;
}

#timer-text {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--primary-color); 
    transition: color 0.3s ease;
}

.secondary-btn {
    background-color: transparent;
    color: var(--text-secondary);
    border: 1px solid var(--border-color);
    padding: 5px 10px;
    border-radius: 8px;
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.secondary-btn:hover {
    background-color: var(--surface-color); /* Hover with surface color */
    color: var(--text-primary);
}

footer {
    text-align: center;
    margin-top: 15px;
    color: var(--text-secondary);
    font-size: 0.8rem;
}

.auth-footer {
    text-align: center;
    margin-top: 5px;
    color: var(--text-secondary);
    font-size: 0.8rem;
}

.developed-by {
    margin-top: 4px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.developed-by span {
    color: var(--primary-color);
    font-weight: 700;
    letter-spacing: 0.5px;
}

.social-links {
    display: inline-flex;
    align-items: center;
    gap: 12px;
    margin-left: 12px;
    vertical-align: middle;
}

.social-links a {
    color: var(--text-secondary);
    display: flex;
    transition: color 0.3s ease;
}

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

.social-icon {
    width: 18px;
    height: 18px;
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.social-links a:hover .social-icon {
    transform: translateY(-2px) scale(1.1);
}

/* --- Global Controls --- */
.global-controls {
    position: fixed;
    top: 20px;
    right: 30px;
    z-index: 1000;
    display: flex;
    align-items: center;
    gap: 15px;
    animation: fadeInUp 1s cubic-bezier(0.16, 1, 0.3, 1) forwards;
}

.language-switcher select {
    appearance: none;
    background-color: var(--surface-color);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    outline: none;
    box-shadow: var(--shadow-main);
    transition: all 0.3s ease;
}

.language-switcher select:hover {
    border-color: var(--primary-color);
}

.theme-switcher {
    box-shadow: var(--shadow-main);
    border-radius: 28px;
}

.theme-switcher input[type="checkbox"] {
    display: none;
}

.toggle-slider {
    display: block;
    width: 50px;
    height: 28px;
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 28px;
    position: relative;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.toggle-slider:before {
    content: "";
    position: absolute;
    top: 2px;
    left: 2px;
    width: 22px;
    height: 22px;
    background-color: var(--text-primary);
    border-radius: 50%;
    transition: transform 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.theme-switcher input:checked + .toggle-slider {
    background-color: var(--primary-color); 
}

.theme-switcher input:checked + .toggle-slider:before {
    transform: translateX(22px);
}

.toggle-slider svg {
    position: absolute;
    width: 16px;
    height: 16px;
    top: 6px;
    transition: opacity 0.3s ease;
    color: var(--text-primary); /* Icons should be primary text color */
}

.toggle-slider .sun { left: 6px; opacity: 0; }
.toggle-slider .moon { right: 6px; opacity: 1; }

.theme-switcher input:checked + .toggle-slider .sun { opacity: 1; }
.theme-switcher input:checked + .toggle-slider .moon { opacity: 0; }

/* --- Confetti --- */
.confetti-piece {
    position: fixed;
    width: 10px;
    height: 10px;
    z-index: 9999;
    pointer-events: none;
}

/* --- Responsive Design & Cross-Platform Adaptability --- */
@media (max-width: 768px) {
    .app-container {
        padding: 25px 20px;
    }
    
    .auth-box {
        padding: 30px 20px;
    }

    h1 {
        font-size: 1.3rem;
    }
    
    .auth-header h1 {
        font-size: 1.8rem;
    }
    
    #iq-score-value {
        font-size: 3rem;
    }

    #level-selection {
        display: flex;
        flex-wrap: wrap;
        gap: 10px;
    }

    #level-selection label {
        margin: 0;
        flex: 1 1 calc(33.333% - 10px);
        text-align: center;
    }

    /* Move theme toggle to bottom right to avoid header overlap on tablets/mobiles */
    .global-controls {
        top: auto;
        bottom: 20px;
        right: 20px;
    }
}

@media (max-width: 480px) {
    body {
        padding: 10px;
    }

    .app-container {
        padding: 20px 15px;
        border-radius: 12px;
    }

    header {
        flex-direction: column;
        gap: 15px;
        align-items: flex-start;
    }

    .header-right {
        width: 100%;
        justify-content: space-between;
    }

    #options-container {
        grid-template-columns: 1fr;
    }

    #level-selection label {
        flex: 1 1 100%; /* Stack difficulty buttons on very small screens */
    }

    .primary-btn {
        width: 100%; /* Full width main buttons for easier tapping */
        padding: 14px 20px; /* Ensure 44px min-height for iOS touch targets */
    }

    .auth-input {
        padding: 18px 40px 8px 12px;
        font-size: 0.95rem;
    }

    .app-logo {
        width: 32px;
    }

    #timer-container {
        width: 35px;
        height: 35px;
    }

    #timer-text {
        font-size: 1rem;
    }

    .progress-bar {
        width: 90px;
    }

    .social-links {
        margin-top: 5px;
        display: block; /* Move links to their own line on tiny screens */
    }
}