/* ==========================================================================
   1. VARIABLES Y CONFIGURACIÓN GENERAL
   ========================================================================== */
:root {
    --bg-primary: #0f172a;
    --bg-surface: #1e293b;
    --bg-surface-hover: #334155;
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --color-primary: #6366f1;
    --color-primary-hover: #4f46e5;
    --color-success: #10b981;
    --color-easy: #4ade80;
    --color-medium: #facc15;
    --color-hard: #f87171;
    --card-back-bg: #312e81;
    --card-front-bg: #4338ca;
    --font-sans: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--bg-primary);
    color: var(--text-main);
    text-wrap: balance;
    display: flex;
    justify-content: center;
    align-items: center;
    line-height: 1.25;
}

#app {
    width: 100%;
    max-width: 800px;
    padding: 1.5rem;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    border: 0;
}

/* ==========================================================================
   2. CONTROL DE PANTALLAS (SCREENS)
   ========================================================================== */
.screen {
    display: none;
    opacity: 0;
    transform: translateY(10px);
    transition: opacity var(--transition-normal), transform var(--transition-normal);
}

.screen.active-screen {
    display: block;
    opacity: 1;
    transform: translateY(0);
}

.screen-container {
    background-color: var(--bg-surface);
    border-radius: 1rem;
    padding: 2rem;
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.3), 0 8px 10px -6px rgba(0, 0, 0, 0.3);
}

.screen-header {
    text-align: center;
    margin-bottom: 2rem;
}

.screen-header h1, .screen-header h2 {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(to right, #a5b4fc, #6366f1);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

.screen-subtitle {
    color: var(--text-muted);
    font-size: 1rem;
}

/* ==========================================================================
   3. COMPONENTES
   ========================================================================== */
/* Botones y niveles de dificultad */
button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    border-radius: 0.5rem;
    transition: all var(--transition-fast);
    padding: 0.75rem 1.5rem;
    font-weight: 600;
    font-size: 1rem;
}

.difficulty-selector h2 {
    font-size: 1.25rem;
    color: var(--text-muted);
    margin-bottom: 1rem;
    text-align: center;
}

.difficulty-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 1rem;
}

.difficulty-button {
    background-color: var(--bg-primary);
    color: var(--text-main);
    border: 2px solid transparent;
}

.difficulty-button:hover {
    transform: translateY(-2px);
}

#easy-button:hover {
    border-color: var(--color-easy);
    color: var(--color-easy);
}

#medium-button:hover {
    border-color: var(--color-medium);
    color: var(--color-medium);
}

#hard-button:hover {
    border-color: var(--color-hard);
    color: var(--color-hard);
}

.actions-buttons {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
    justify-content: center;
}

#play-again-button {
    background-color: var(--color-primary);
    color: var(--text-main);
}

#play-again-button:hover {
    background-color: var(--color-primary-hover);
}

#cancel-game-button, #back-menu-button {
    background-color: transparent;
    color: var(--text-muted);
    border: 1px solid var(--bg-surface-hover);
}

#cancel-game-button:hover, #back-menu-button:hover {
    background-color: var(--bg-surface-hover);
    color: var(--text-main);
}

/* Cabecera del juego activo */
.game-header {
    display: flex;
    justify-content: space-around;
    background-color: var(--bg-primary);
    padding: 1rem;
    border-radius: 0.75rem;
    margin-bottom: 2rem;
}

.game-stat {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.game-stat .label {
    font-size: 0.75rem;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 0.05em;
}

.game-stat span:last-child {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--color-primary);
}

/* Puntuación de resultados */
.results-summary {
    text-align: center;
    margin-bottom: 2rem;
}

.results-label {
    color: var(--text-muted);
    text-transform: uppercase;
    font-size: 1.25rem;
    letter-spacing: 0.1em;
}

.final-score {
    font-size: 4rem;
    font-weight: 900;
    color: var(--color-success);
}

/* ==========================================================================
   4. TABLERO Y LÓGICA DE OCULTAR/VOLTEAR CARTAS
   ========================================================================== */
.game-board {
    display: grid;
    gap: 0.75rem;
    margin: 0 auto;
    width: 100%;
    max-width: 100%;
}

/* Botón del contenedor principal */
.card {
    aspect-ratio: 3 / 4;
    position: relative;
    padding: 0;
    background: transparent;
    border: none;
    outline: none;
    perspective: 1000px; /* Habilita el efecto tridimensional del volteo */
    width: 100%;         /* Forzamos a que ocupe todo el ancho de su celda grid */
    height: 100%;        /* Forzamos a que mantenga el alto proporcional correspondiente */
    display: block;      /* Puesto a block para asegurar que aspect-ratio funciona con grid */
    transform: scale(1);
    transition: transform var(--transition-fast);
}

/* Elevación sutil al pasar el ratón por encima (solo si no está emparejada) */
.card:not(.card-disabled):hover {
    transform: translateY(-4px);
    z-index: 10; /* Evita que la carta que se eleva quede por debajo de sus vecinas */
}

/* CONTENEDOR INTERNO: Es el elemento que físicamente va a rotar 180 grados */
.card-inner {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border-radius: 0.75rem;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.3);
    
    /* Propiedades nativas fundamentales para la rotación 3D */
    transform-style: preserve-3d; 
    transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* LÓGICA DEL GIRO: Cuando se añade la clase .card-flipped, ejecutamos el giro sobre el eje Y */
.card.card-flipped .card-inner {
    transform: rotateY(180deg);
}

/* Propiedades compartidas por ambas caras de las cartas */
.card-front, .card-back {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border-radius: 0.75rem;
    
    /* Oculta la cara trasera cuando está de espaldas a la pantalla */
    backface-visibility: hidden; 
    -webkit-backface-visibility: hidden;
    
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
}

/* CARA REVERSO: Se ve cuando está boca abajo y está oculto el contenido */
.card-back {
    background: linear-gradient(135deg, #1e1b4b 0%, #311042 100%);
    border: 2px solid rgba(99, 102, 241, 0.3);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

/* Brillo en el reverso cuando el cursor pasa por encima */
.card:not(.card-disabled):hover .card-back {
    border-color: rgba(99, 102, 241, 0.8);
    box-shadow: 0 0 15px rgba(99, 102, 241, 0.5);
}

/* CARA ANVERSO: Se ve cuando está boca arriba y muestra el contenido */
.card-front {
    background-color: var(--card-front-bg);
    border: 2px solid var(--color-primary);
    font-size: 2.5rem;
    user-select: none;
    
    /* Inicialmente está invertida para que se vea bien al completar el giro de 180° */
    transform: rotateY(180deg); 
}

/* ESTADO: Pareja encontrada (matched) */
.card-matched .card-inner {
    animation: matchPulse3D 0.4s ease-out forwards;
}

.card-matched .card-front {
    background-color: rgba(16, 185, 129, 0.15);
    border: 2px solid var(--color-success);
    filter: drop-shadow(0 0 8px rgba(16, 185, 129, 0.6));
}

/* Bloqueo del puntero para evitar clicks repetidos */
.card-disabled {
    pointer-events: none;
    cursor: default;
}

/* ==========================================================================
   5. ANIMACIONES 3D
   ========================================================================== */
@keyframes matchPulse3D {
    0% {
        transform: rotateY(180deg) scale(1);
    }
    50% {
        transform: rotateY(180deg) scale(1.1);
        box-shadow: 0 0 20px rgba(16, 185, 129, 0.6);
    }
    100% {
        transform: rotateY(180deg) scale(1);
    }
}

/* ==========================================================================
   6. MEDIAQUERIES
   ========================================================================== */
/* Ajustes adaptativos para contenidos en pantallas muy pequeñas */
@media (max-width: 480px) {
    .card-front {
        font-size: 1.25rem;
    }
    .game-board {
        gap: 0.4rem;
    }
    .screen-container {
        padding: 1.25rem;
    }
}