:root {
    --pastel-blue: #a3bffa;
    --pastel-pink: #f4a7b9;
    --pastel-green: #b5e4ca;
    --pastel-purple: #d4b2d8;
    --pastel-yellow: #fde68a;
    --pastel-gray: #e5e7eb;
    --text-color: #555;
    --dark-pastel-blue: #7a92e0;
    --dark-pastel-pink: #e07b92;
    --dark-pastel-green: #8dc4a5;
    --dark-pastel-purple: #b08bb5;
    --dark-pastel-yellow: #d6b958;
    --dark-pastel-gray: #3a3a4a;
    --dark-text-color: #d0d0d0;
    --text-xs: 0.75rem;
    --text-sm: 0.875rem;
    --text-base: 1rem;
    --text-lg: 1.125rem;
    --text-xl: 1.25rem;
    --text-2xl: 1.5rem;
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --radius-sm: 8px;
    --radius-md: 16px;
    --radius-lg: 25px;
    --radius-full: 9999px;
}

* {
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
}

body {
    margin: 0;
    font-family: 'Poppins', -apple-system, BlinkMacSystemFont, sans-serif;
    background: #f5f5f5;
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    overflow-y: auto;
    padding: var(--spacing-md) var(--spacing-sm);
    position: relative;
    transition: background 0.3s ease, color 0.3s ease;
    padding-top: env(safe-area-inset-top, 0);
    padding-bottom: env(safe-area-inset-bottom, 0);
    padding-left: env(safe-area-inset-left, 0);
    padding-right: env(safe-area-inset-right, 0);
}

body.dark-mode {
    background: #2a2a3a;
    color: var(--dark-text-color);
}

.container {
    text-align: center;
    padding: var(--spacing-lg) var(--spacing-md);
    width: 100%;
    max-width: 480px;
    position: relative;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
}

h1 {
    font-size: var(--text-xl);
    margin: 0;
    color: var(--pastel-blue);
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 600;
}

body.dark-mode h1 {
    color: var(--dark-pastel-blue);
}

.dark-mode-btn {
    background: none;
    border: none;
    font-size: var(--text-xl);
    cursor: pointer;
    padding: var(--spacing-sm);
    border-radius: var(--radius-full);
    color: var(--pastel-blue);
    transition: transform 0.2s ease, background-color 0.2s ease;
}

.dark-mode-btn:hover, .dark-mode-btn:active {
    transform: scale(1.1);
    background-color: rgba(163, 191, 250, 0.1);
}

body.dark-mode .dark-mode-btn {
    color: var(--dark-pastel-blue);
}

body.dark-mode .dark-mode-btn:hover, 
body.dark-mode .dark-mode-btn:active {
    background-color: rgba(122, 146, 224, 0.1);
}

.score-board {
    display: flex;
    justify-content: space-between;
    margin-bottom: var(--spacing-md);
    gap: var(--spacing-md);
}

.score-card {
    flex: 1;
    font-size: var(--text-base);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    background: var(--pastel-gray);
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.score-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

body.dark-mode .score-card {
    background: var(--dark-pastel-gray);
    color: var(--dark-text-color);
}

.progress-container {
    position: relative;
    height: 8px;
    background-color: var(--pastel-gray);
    border-radius: var(--radius-full);
    margin: var(--spacing-md) 0;
    overflow: hidden;
}

body.dark-mode .progress-container {
    background-color: var(--dark-pastel-gray);
}

#progress-bar {
    position: absolute;
    height: 100%;
    background-color: var(--pastel-blue);
    border-radius: var(--radius-full);
    transition: width 0.3s ease;
}

body.dark-mode #progress-bar {
    background-color: var(--dark-pastel-blue);
}

.progress-card {
    font-size: var(--text-sm);
    padding: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
    color: var(--text-color);
}

body.dark-mode .progress-card {
    color: var(--dark-text-color);
}

.mode-switch-card {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    border-radius: var(--radius-lg);
    background: var(--pastel-gray);
    font-size: var(--text-sm);
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
}

body.dark-mode .mode-switch-card {
    background: var(--dark-pastel-gray);
    color: var(--dark-text-color);
}

.switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: #ccc;
    transition: 0.4s;
    border-radius: 24px;
}

.slider:before {
    position: absolute;
    content: "";
    height: 20px;
    width: 20px;
    left: 2px;
    bottom: 2px;
    background: #fff;
    transition: 0.4s;
    border-radius: 50%;
}

input:checked + .slider {
    background: var(--pastel-blue);
}

body.dark-mode input:checked + .slider {
    background: var(--dark-pastel-blue);
}

input:checked + .slider:before {
    transform: translateX(26px);
}

.flashcard-container {
    position: relative;
    width: 100%;
    margin: var(--spacing-lg) 0;
}

.flashcard {
    width: 100%;
    aspect-ratio: 3/4;
    perspective: 1000px;
    position: relative;
    margin: 0 auto;
    max-width: 320px;
    transform: translateZ(0);
}

.front, .back {
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: #fff;
    border-radius: var(--radius-lg);
    backface-visibility: hidden;
    transition: transform 0.5s ease;
    will-change: transform;
    -webkit-backface-visibility: hidden;
    box-shadow: 0 8px 16px rgba(0,0,0,0.1);
    padding: var(--spacing-lg);
    font-size: var(--text-xl);
    text-align: center;
    color: var(--text-color);
    user-select: none;
    overflow-wrap: break-word;
    word-wrap: break-word;
    overflow: hidden;
    text-overflow: ellipsis;
}

body.dark-mode .front,
body.dark-mode .back {
    background: #3d3d50;
    color: var(--dark-text-color);
    box-shadow: 0 8px 16px rgba(0,0,0,0.3);
}

.back {
    max-height: 100%;
    overflow-y: auto;
}

.front::before {
    content: '';
    position: absolute;
    top: var(--spacing-md);
    right: var(--spacing-md);
    width: 24px;
    height: 24px;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23a3bffa' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M7 17l9.2-9.2M17 17V7H7'/%3E%3C/svg%3E");
    background-size: contain;
    opacity: 0.5;
}

body.dark-mode .front::before {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%237a92e0' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M7 17l9.2-9.2M17 17V7H7'/%3E%3C/svg%3E");
}

.front {
    transform: rotateY(0deg);
    z-index: 2;
}

.back {
    transform: rotateY(180deg);
}

.flashcard.flipped .front {
    transform: rotateY(180deg);
}

.flashcard.flipped .back {
    transform: rotateY(0deg);
}

.translation {
    margin: var(--spacing-sm) 0;
    font-size: var(--text-lg);
    max-width: 100%;
    overflow-wrap: break-word;
}

.divider {
    width: 50px;
    height: 2px;
    background-color: var(--pastel-gray);
    margin: var(--spacing-sm) 0;
}

body.dark-mode .divider {
    background-color: var(--dark-pastel-gray);
}

.flip-hint {
    position: absolute;
    bottom: var(--spacing-md);
    left: 0;
    right: 0;
    text-align: center;
    font-size: var(--text-xs);
    color: var(--pastel-blue);
    opacity: 0.7;
    animation: pulse 2s infinite;
}

body.dark-mode .flip-hint {
    color: var(--dark-pastel-blue);
}

@keyframes pulse {
    0% { opacity: 0.5; }
    50% { opacity: 1; }
    100% { opacity: 0.5; }
}

.flashcard.correct {
    animation: correct-answer 1s;
}

.flashcard.incorrect {
    animation: incorrect-answer 1s;
}

@keyframes correct-answer {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); background-color: var(--pastel-green); }
}

@keyframes incorrect-answer {
    0%, 100% { transform: scale(1); }
    10%, 30%, 50%, 70%, 90% { transform: translateX(-5px); }
    20%, 40%, 60%, 80% { transform: translateX(5px); }
}

.slide-out-left {
    animation: slideOutLeft 0.3s forwards;
}

.slide-in-right {
    animation: slideInRight 0.3s forwards;
}

.slide-out-right {
    animation: slideOutRight 0.3s forwards;
}

.slide-in-left {
    animation: slideInLeft 0.3s forwards;
}

@keyframes slideOutLeft {
    from { transform: translateX(0); opacity: 1; }
    to { transform: translateX(-50px); opacity: 0; }
}

@keyframes slideInRight {
    from { transform: translateX(50px); opacity: 0; }
    to { transform: translateX(0); opacity: 1; }
}

@keyframes slideOutRight {
    from { transform: translateX(0); opacity: 1; }
    to { transform: translateX(50px); opacity: 0; }
}

@keyframes slideInLeft {
    from { transform: translateX(-50px); opacity: 0; }
    to { transform: translateX(0); opacity: 1; }
}

.feedback-buttons {
    display: flex;
    justify-content: space-around;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
}

.action-btn {
    flex: 1;
    padding: var(--spacing-md);
    font-size: var(--text-base);
    border: none;
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    color: #fff;
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 500;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.action-btn:active {
    transform: scale(0.96);
}

.correct-btn {
    background: var(--pastel-green);
}

body.dark-mode .correct-btn {
    background: var(--dark-pastel-green);
}

.correct-btn:hover, .correct-btn:focus {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.incorrect-btn {
    background: var(--pastel-pink);
}

body.dark-mode .incorrect-btn {
    background: var(--dark-pastel-pink);
}

.incorrect-btn:hover, .incorrect-btn:focus {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.navigation-buttons {
    display: flex;
    justify-content: space-between;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
    position: relative;
    z-index: 10;
}

.nav-btn {
    flex: 1;
    padding: var(--spacing-md);
    max-height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.prev-btn {
    background: var(--pastel-purple);
}

body.dark-mode .prev-btn {
    background: var(--dark-pastel-purple);
}

.prev-btn:hover, .prev-btn:focus {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.next-btn {
    background: var(--pastel-blue);
}

body.dark-mode .next-btn {
    background: var(--dark-pastel-blue);
}

.next-btn:hover, .next-btn:focus {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

#confetti-container {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    overflow: hidden;
    z-index: 1000;
}

.confetti {
    position: absolute;
    top: -20px;
    font-size: var(--text-xl);
    opacity: 0.9;
    animation: fall 2s linear forwards;
    z-index: 1000;
}

@keyframes fall {
    0% { transform: translateY(-20px) rotate(0deg); opacity: 1; }
    50% { transform: translateY(50vh) rotate(180deg); }
    100% { transform: translateY(100vh) rotate(360deg); opacity: 0; }
}

@media (max-width: 350px) {
    :root {
        --text-xs: 0.7rem;
        --text-sm: 0.8rem;
        --text-base: 0.9rem;
        --text-lg: 1rem;
        --text-xl: 1.1rem;
        --text-2xl: 1.3rem;
    }
    
    .container {
        padding: var(--spacing-sm);
    }
    
    .score-card, .action-btn {
        padding: var(--spacing-sm);
    }
    
    .front, .back {
        padding: var(--spacing-md);
    }
}

@media (min-width: 768px) {
    :root {
        --text-xs: 0.8rem;
        --text-sm: 0.95rem;
        --text-base: 1.1rem;
        --text-lg: 1.25rem;
        --text-xl: 1.5rem;
        --text-2xl: 2rem;
    }
    
    .container {
        padding: var(--spacing-xl);
        max-width: 550px;
    }
    
    .flashcard {
        max-width: 380px;
    }
}

@supports (-webkit-overflow-scrolling: touch) {
    body {
        height: -webkit-fill-available;
    }
    html {
        height: -webkit-fill-available;
    }
}

* {
    -webkit-tap-highlight-color: transparent;
}