@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&family=JetBrains+Mono:wght@400;500&display=swap');
    
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary: #667eea;          /* azul principal */
    --primary-dark: #5a67d8;     /* azul más oscuro */
    --primary-light: #7f9cf5;    /* azul más claro */
    --secondary: #764ba2;        /* violeta secundario */
    --accent: #9f7aea;           /* violeta-acento */
    --dark: #1f2937;             /* gris oscuro para textos */
    --gray: #6b7280;             /* gris */
    --light-gray: #f3f4f6;       /* gris claro */
    --white: #ffffff;

    /* Sombras */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

    /* Gradientes */
    --gradient-primary: linear-gradient(135deg, #667eea 0%, #764ba2 100%); /* azul → violeta */
    --gradient-success: linear-gradient(135deg, #667eea 0%, #5a67d8 100%); /* botón mostrar solución */
    --gradient-warm: linear-gradient(135deg, #764ba2 0%, #9f7aea 100%);    /* botón clases particulares */
}


body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    position: relative;
    overflow-x: hidden;
}

body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: 
    radial-gradient(circle at 20% 50%, rgba(120, 119, 198, 0.3) 0%, transparent 50%),
    radial-gradient(circle at 80% 80%, rgba(255, 119, 198, 0.3) 0%, transparent 50%),
    radial-gradient(circle at 40% 20%, rgba(255, 219, 98, 0.2) 0%, transparent 50%);
    pointer-events: none;
    z-index: 1;
}

/* Animated Background Particles */
@keyframes float {
    0%, 100% { transform: translateY(0) rotate(0deg); opacity: 0.5; }
    50% { transform: translateY(-20px) rotate(180deg); opacity: 1; }
}

.bg-decoration {
    position: fixed;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 0;
}

.bg-decoration::before,
.bg-decoration::after {
    content: '';
    position: absolute;
    border-radius: 50%;
    animation: float 20s infinite ease-in-out;
}

.bg-decoration::before {
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, rgba(139, 92, 246, 0.1) 0%, transparent 70%);
    top: -200px;
    right: -200px;
}

.bg-decoration::after {
    width: 600px;
    height: 600px;
    background: radial-gradient(circle, rgba(16, 185, 129, 0.1) 0%, transparent 70%);
    bottom: -300px;
    left: -300px;
    animation-delay: 10s;
}

/* Header */
.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 70px;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 30px;
    box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
}

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

.header-logo .icon {
    width: 40px;
    height: 40px;
    background: var(--gradient-primary);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    color: white;
    font-weight: bold;
    box-shadow: var(--shadow-md);
}

.header-title {
    font-size: 20px;
    font-weight: 700;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

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

.btn-header {
    padding: 10px 20px;
    border: none;
    border-radius: 12px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    gap: 8px;
}

.btn-back {
    background: rgba(102, 126, 234, 0.1);
    color: #667eea;
}

.btn-back:hover {
    background: rgba(102, 126, 234, 0.2);
    transform: translateX(-3px);
}

.btn-menu {
    background: var(--gradient-primary);
    color: white;
    display: none;
    box-shadow: var(--shadow-md);
}

.btn-menu:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

/* Sidebar */
.sidebar {
    position: fixed;
    top: 70px;
    left: 0;
    width: 280px;
    height: calc(100vh - 70px);
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-right: 1px solid rgba(255, 255, 255, 0.2);
    overflow-y: auto;
    padding: 30px 20px;
    z-index: 999;
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.sidebar::-webkit-scrollbar {
    width: 6px;
}

.sidebar::-webkit-scrollbar-track {
    background: rgba(0, 0, 0, 0.05);
    border-radius: 3px;
}

.sidebar::-webkit-scrollbar-thumb {
    background: var(--gradient-primary);
    border-radius: 3px;
}

.sidebar-title {
    font-size: 14px;
    font-weight: 600;
    color: var(--gray);
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 25px;
    padding-left: 10px;
}

.sidebar details {
    margin-bottom: 15px;
    background: white;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: all 0.3s ease;
}

.sidebar details[open] {
    box-shadow: var(--shadow-md);
    background: linear-gradient(145deg, #ffffff 0%, #f9fafb 100%);
}

.sidebar summary {
    cursor: pointer;
    padding: 15px 20px;
    font-weight: 600;
    color: var(--dark);
    transition: all 0.3s ease;
    user-select: none;
    list-style: none;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.sidebar summary::-webkit-details-marker {
    display: none;
}

.sidebar summary::after {
    content: '▶';
    font-size: 12px;
    transition: transform 0.3s ease;
    color: var(--gray);
}

.sidebar details[open] summary::after {
    transform: rotate(90deg);
}

.sidebar summary:hover {
    background: linear-gradient(90deg, rgba(102, 126, 234, 0.1) 0%, rgba(139, 92, 246, 0.1) 100%);
    padding-left: 25px;
}

.sidebar ul {
    list-style: none;
    padding: 0 20px 15px;
    margin: 0;
}

.sidebar ul li {
    margin: 5px 0;
}

.sidebar ul li a {
    display: block;
    padding: 10px 15px;
    color: var(--gray);
    text-decoration: none;
    border-radius: 8px;
    transition: all 0.3s ease;
    font-size: 14px;
    position: relative;
    overflow: hidden;
}

.sidebar ul li a::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 3px;
    height: 0;
    background: var(--gradient-primary);
    transition: height 0.3s ease;
}

.sidebar ul li a:hover {
    background: linear-gradient(90deg, rgba(102, 126, 234, 0.1) 0%, transparent 100%);
    color: #667eea;
    padding-left: 25px;
}

.sidebar ul li a:hover::before {
    height: 70%;
}

/* Content */
.content {
    margin-left: 280px;
    padding: 80px 30px 30px; /* antes era 100px */
    min-height: 100vh;
    position: relative;
    z-index: 2;
}

.tema {
    margin-bottom: 60px;
}

.tema-header {
    text-align: center;
    margin: 10px 0 10px;
    position: relative;
}

.tema-header h2 {
    font-size: 32px;
    font-weight: 800;
    color: #ffffff; /* blanco puro */
    margin-bottom: 10px;
    animation: fadeInUp 0.6s ease;
}



.tema-header::before,
.tema-header::after {
    content: '';
    position: absolute;
    top: 50%;
    width: 100px;
    height: 2px;
    background: linear-gradient(90deg, transparent, rgba(102, 126, 234, 0.3), transparent);
}

.tema-header::before {
    left: 50%;
    transform: translateX(-200px) translateY(-50%);
}

.tema-header::after {
    right: 50%;
    transform: translateX(200px) translateY(-50%);
}

/* Exercise Cards */
.ejercicio {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 30px;
    margin-bottom: 30px;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.1);
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    position: relative;
    overflow: hidden;
    display: flex;
    gap: 30px;
    align-items: flex-start;
    scroll-margin-top: 100px; /* compensa header fijo */
}

.ejercicio::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transition: transform 0.4s ease;
}

.ejercicio:hover {
    transform: translateY(-5px);
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.15);
}

.ejercicio:hover::before {
    transform: scaleX(1);
}

.ejercicio-contenido {
    flex: 1;
    text-align: center;
}

.ejercicio-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 15px;
    margin-bottom: 20px;
}

.ejercicio-numero {
    width: 40px;
    height: 40px;
    background: var(--gradient-primary);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-weight: bold;
    font-size: 18px;
    box-shadow: var(--shadow-md);
}

.ejercicio-contenido h3 {
    font-size: 20px;
    font-weight: 700;
    color: var(--dark);
    margin: 0;
}

.ejercicio-imagen {
    background: white;
    border-radius: 12px;
    padding: 15px;
    margin: 20px 0;
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.06);
    transition: all 0.3s ease;
}

.ejercicio-imagen:hover {
    box-shadow: inset 0 4px 8px rgba(0, 0, 0, 0.1);
}

.ejercicio-imagen img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    display: block;
}

.ejercicio-actions {
    display: flex;
    gap: 15px;
    justify-content: center;
    flex-wrap: wrap;
}

.ejercicio.highlight {
    box-shadow: 0 0 0 4px rgba(102, 126, 234, 0.6), 0 10px 40px rgba(0, 0, 0, 0.1);
    transition: box-shadow 0.8s ease;
}

.ejercicio-video {
    margin-top: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
}


.ejercicio-video iframe {
    width: 100%;
    max-width: 400px;   /* más estrecho, estilo móvil */
    height: 533px;      /* más alto para 9:16 */
    border-radius: 16px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.15);
    border: 2px solid rgba(255, 255, 255, 0.2);
    overflow: hidden;
}



/* Buttons */
.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 12px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 8px;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.btn:hover::before {
    width: 300px;
    height: 300px;
}

.btn-primary {
    background: var(--gradient-success);
    color: white;
    box-shadow: 0 4px 15px rgba(79, 70, 229, 0.4);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(79, 70, 229, 0.4);
}

.btn-premium {
    background: var(--gradient-warm);
    color: white;
    box-shadow: 0 4px 15px rgba(168, 14, 245, 0.3);
    width: 100%;
    margin-top: 15px;
    padding: 15px;
    font-size: 15px;
    position: relative;
}

.btn-premium::after {
    content: '⭐';
    position: absolute;
    right: 20px;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); opacity: 1; }
    50% { transform: scale(1.2); opacity: 0.8; }
}

.btn-premium:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 25px rgba(168, 14, 245, 0.3);
}

/* Solution */
.solucion {
    flex: 1;
    opacity: 0;
    transform: translateX(20px);
    transition: all 0.5s ease;
    display: none;
}

.solucion.visible {
    opacity: 1;
    transform: translateX(0);
    display: block;
}

.solucion-card {
    background: linear-gradient(145deg, #f0fdf4 0%, #dcfce7 100%);
    border-radius: 12px;
    padding: 20px;
    border: 2px solid #10b981;
    box-shadow: 0 4px 15px rgba(16, 185, 129, 0.1);
}

.solucion-header {
    font-size: 14px;
    font-weight: 600;
    color: #10b981;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 15px;
    text-align: center;
}

.solucion img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    box-shadow: var(--shadow-md);
}

/* Popup Modal */
#popup {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(10px);
    z-index: 2000;
    justify-content: center;
    align-items: center;
    animation: fadeIn 0.3s ease;
}

#popup.active {
    display: flex;
}

.popup-box {
    background: white;
    border-radius: 24px;
    padding: 40px;
    width: 90%;
    max-width: 480px;
    text-align: center;
    box-shadow: 0 25px 50px rgba(0, 0, 0, 0.25);
    animation: slideUp 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    position: relative;
    overflow: hidden;
}

.popup-box::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -50%;
    width: 200%;
    height: 200%;
    background: radial-gradient(circle, rgba(102, 126, 234, 0.1) 0%, transparent 70%);
    animation: rotate 20s linear infinite;
}

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

.popup-icon {
    width: 80px;
    height: 80px;
    background: var(--gradient-warm);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 20px;
    font-size: 40px;
    box-shadow: 0 10px 30px rgba(245, 158, 11, 0.3);
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}

.popup-box h3 {
    font-size: 28px;
    font-weight: 800;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 15px;
    position: relative;
    z-index: 1;
}

.popup-box p {
    color: var(--gray);
    margin-bottom: 30px;
    line-height: 1.6;
    position: relative;
    z-index: 1;
}

.popup-inputs {
    position: relative;
    z-index: 1;
}

.popup-input {
    width: 100%;
    padding: 15px 20px;
    margin-bottom: 15px;
    border: 2px solid #e5e7eb;
    border-radius: 12px;
    font-size: 15px;
    transition: all 0.3s ease;
    background: white;
}

.popup-input:focus {
    outline: none;
    border-color: #667eea;
    box-shadow: 0 0 0 4px rgba(102, 126, 234, 0.1);
}

.popup-actions {
    display: flex;
    gap: 15px;
    margin-top: 20px;
    position: relative;
    z-index: 1;
}

.popup-actions button {
    flex: 1;
    padding: 15px;
    border: none;
    border-radius: 12px;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

.btn-enviar {
    background: var(--gradient-primary);
    color: white;
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.3);
}

.btn-enviar:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.4);
}

.btn-cancelar {
    background: #f3f4f6;
    color: var(--gray);
}

.btn-cancelar:hover {
    background: #e5e7eb;
}

/* Footer */
footer {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    color: var(--gray);
    text-align: center;
    padding: 20px;
    font-size: 14px;
    margin-top: 60px;
    margin-left: 280px;
    border-radius: 20px 20px 0 0;
    box-shadow: 0 -5px 30px rgba(0, 0, 0, 0.1);
    position: relative;
    z-index: 2;
}

footer .footer-content {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
}

footer .footer-icon {
    font-size: 20px;
    animation: pulse 2s infinite;
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

@keyframes slideUp {
    from { 
    opacity: 0;
    transform: translateY(30px);
    }
    to { 
    opacity: 1;
    transform: translateY(0);
    }
}

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

/* Responsive Design */
@media (max-width: 1024px) {
    .sidebar {
    transform: translateX(-100%);
    }

    .sidebar.active {
    transform: translateX(0);
    box-shadow: 5px 0 30px rgba(0, 0, 0, 0.2);
    }

    .content {
    margin-left: 0;
    }

    footer {
    margin-left: 0;
    }

    .btn-menu {
    display: flex;
    }
}

@media (max-width: 768px) {
    .header {
    padding: 0 20px;
    }

    .header-title {
    font-size: 16px;
    }

    .content {
    padding: 90px 20px 20px;
    }

    .ejercicio {
    flex-direction: column;
    padding: 20px;
    }

    .solucion {
    margin-top: 20px;
    }

    .tema-header h2 {
    font-size: 24px;
    }

    .tema-header::before,
    .tema-header::after {
    display: none;
    }

    .popup-box {
    padding: 30px 20px;
    margin: 20px;
    }
}

/* Loading Animation */
.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid rgba(255, 255, 255, 0.3);
    border-radius: 50%;
    border-top-color: white;
    animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Tooltips */
[data-tooltip] {
    position: relative;
}

[data-tooltip]:hover::after {
    content: attr(data-tooltip);
    position: absolute;
    bottom: 100%;
    left: 50%;
    transform: translateX(-50%);
    background: var(--dark);
    color: white;
    padding: 8px 12px;
    border-radius: 8px;
    font-size: 12px;
    white-space: nowrap;
    z-index: 1000;
    pointer-events: none;
    opacity: 0;
    animation: fadeIn 0.3s forwards;
    margin-bottom: 5px;
}