/* Estilos generales de la sección de investigación */
.investigacion-section {
    padding: 4rem 0;
    background-color: #f8f9fa;
}

/* Contenedor principal */
.investigacion-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Encabezado de la sección */
.investigacion-header {
    text-align: center;
    margin-bottom: 3rem;
}

.investigacion-header h2 {
    font-size: 2.2rem;
    color: #2c3e50;
    margin-bottom: 1rem;
    position: relative;
    display: inline-block;
}

.investigacion-header h2::after {
    content: '';
    position: absolute;
    width: 60px;
    height: 4px;
    background: linear-gradient(90deg, #4a90e2, #9013fe);
    bottom: -10px;
    left: 50%;
    transform: translateX(-50%);
    border-radius: 2px;
}

.investigacion-header p {
    color: #6c757d;
    font-size: 1.1rem;
    max-width: 700px;
    margin: 0 auto;
    line-height: 1.6;
}

/* Contenedor de años */
.anios-container {
    max-width: 900px;
    margin: 0 auto;
    background: white;
    border-radius: 12px;
    box-shadow: 0 5px 30px rgba(0, 0, 0, 0.08);
    overflow: hidden;
}

/* Estilos para los bloques de año */
.anio-bloque {
    border-bottom: 1px solid #f0f0f0;
    transition: all 0.3s ease;
}

.anio-bloque:last-child {
    border-bottom: none;
}

.anio-btn {
    width: 100%;
    background: none;
    border: none;
    font-size: 1.2rem;
    font-weight: 600;
    text-align: left;
    color: #2c3e50;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem 2rem;
    transition: all 0.3s ease;
    position: relative;
    background-color: #fff;
}

.year-text {
    font-size: 1.3rem;
    font-weight: 700;
    color: #2c3e50;
}

.year-info {
    display: flex;
    align-items: center;
    gap: 15px;
}

.anio-btn:hover {
    background-color: #f8f9fa;
    color: #4a90e2;
}

.anio-btn.activo {
    background-color: #f8f9fa;
    color: #4a90e2;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}

.arrow-icon {
    font-size: 1rem;
    transition: transform 0.3s ease;
    color: #6c757d;
}

.anio-btn.activo .arrow-icon {
    transform: rotate(180deg);
    color: #4a90e2;
}

.anio-btn.activo .year-text {
    color: #4a90e2;
}

.articulo-count {
    background: linear-gradient(135deg, #e9ecef, #dee2e6);
    color: #495057;
    font-size: 0.85rem;
    padding: 4px 12px;
    border-radius: 20px;
    font-weight: 600;
    letter-spacing: 0.3px;
}

.anio-btn.activo .articulo-count {
    background: linear-gradient(135deg, #e3f2fd, #bbdefb);
    color: #1976d2;
}

/* Lista de artículos */
.articulos-lista {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    background-color: #f8f9fa;
}

.articulos-lista.activo {
    max-height: 2000px;
    padding: 0 2rem 1.5rem;
}

/* Items de artículos */
.articulo-item {
    background-color: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
    margin-bottom: 1rem;
    transition: all 0.3s ease;
    border-left: 4px solid transparent;
}

.articulo-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 20px rgba(0, 0, 0, 0.1);
    border-left-color: #4a90e2;
}

.articulo-item h4 {
    font-size: 1.1rem;
    color: #2c3e50;
    margin: 0 0 0.5rem 0;
    font-weight: 600;
    line-height: 1.4;
}

.articulo-autores {
    color: #6c757d;
    font-size: 0.9rem;
    margin: 0 0 1rem 0;
    font-style: italic;
}

.articulo-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 1rem;
    padding-top: 0.8rem;
    border-top: 1px solid #f0f0f0;
}

.articulo-fecha {
    font-size: 0.85rem;
    color: #868e96;
}

/* Botones */
.btn-link {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    color: #4a90e2;
    text-decoration: none;
    font-weight: 500;
    font-size: 0.95rem;
    transition: all 0.3s ease;
    padding: 0.5rem 0;
    position: relative;
}

.btn-link::after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    bottom: 0;
    left: 0;
    background-color: #4a90e2;
    transition: width 0.3s ease;
}

.btn-link:hover {
    color: #1976d2;
    gap: 10px;
}

.btn-link:hover::after {
    width: 100%;
}

.btn-link i {
    font-size: 0.9em;
    transition: transform 0.3s ease;
}

.btn-link:hover i {
    transform: translateX(3px);
}


/* Responsive */
@media (max-width: 768px) {
    .investigacion-header h2 {
        font-size: 1.8rem;
    }
    
    .anio-btn {
        padding: 1rem 1.5rem;
        font-size: 1.1rem;
    }
    
    .articulos-lista.activo {
        padding: 0 1rem 1rem;
    }
    
    .articulo-item {
        padding: 1.2rem;
    }
    
    .articulo-item h4 {
        font-size: 1rem;
    }
    
    .articulo-autores {
        font-size: 0.85rem;
    }
}

/* Estilos para el estado de carga */
.loading-state {
    text-align: center;
    padding: 2rem;
    color: #6c757d;
}

.loading-spinner {
    display: inline-block;
    width: 2rem;
    height: 2rem;
    border: 3px solid rgba(0, 0, 0, 0.1);
    border-radius: 50%;
    border-top-color: #4a90e2;
    animation: spin 1s ease-in-out infinite;
    margin-bottom: 1rem;
}

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

/* Mensaje cuando no hay artículos */
.no-articles {
    text-align: center;
    padding: 2rem;
    color: #6c757d;
    font-style: italic;
}