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

body {
    font-family: Arial, sans-serif;
    line-height: 1.6;
    background-color: #f0f2f5;
}

/* Sidebar styles */
.sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: 280px;
    height: 100vh;
    background-color: #2c3e50;
    color: white;
    transition: transform 0.3s ease;
    z-index: 1000;
    overflow-y: auto;
}

.sidebar.collapsed {
    transform: translateX(-280px);
}

.sidebar-header {
    padding: 20px;
    background-color: #34495e;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.sidebar-header h2 {
    font-size: 1.2rem;
    margin-bottom: 5px;
}

.sidebar-header p {
    font-size: 0.85rem;
    color: #bdc3c7;
}

.lesson-menu {
    padding: 10px 0;
}

.lesson-group {
    margin-bottom: 5px;
}

.lesson-group-header {
    padding: 12px 20px;
    font-weight: 600;
    font-size: 0.95rem;
    color: #ecf0f1;
    background-color: rgba(52, 73, 94, 0.5);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: background-color 0.2s;
}

.lesson-group-header:hover {
    background-color: rgba(52, 73, 94, 0.8);
}

.lesson-group-toggle {
    transition: transform 0.3s;
}

.lesson-group.collapsed .lesson-group-toggle {
    transform: rotate(-90deg);
}

.lesson-group-content {
    max-height: 1000px;
    overflow: hidden;
    transition: max-height 0.3s ease;
}

.lesson-group.collapsed .lesson-group-content {
    max-height: 0;
}

.lesson-item {
    padding: 12px 20px 12px 35px;
    cursor: pointer;
    transition: background-color 0.2s;
    border-left: 3px solid transparent;
}

.lesson-item:hover {
    background-color: #34495e;
}

.lesson-item.active {
    background-color: #3498db;
    border-left-color: #2ecc71;
}

.lesson-item-title {
    font-weight: 500;
    margin-bottom: 3px;
    font-size: 0.9rem;
}

.lesson-item-count {
    font-size: 0.8rem;
    color: #bdc3c7;
}

/* Toggle button */
.sidebar-toggle {
    position: fixed;
    top: 20px;
    left: 20px;
    width: 50px;
    height: 50px;
    background-color: #3498db;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    z-index: 999;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 5px;
    transition: left 0.3s ease, background-color 0.2s;
}

.sidebar-toggle:hover {
    background-color: #2980b9;
}

.sidebar-toggle span {
    width: 24px;
    height: 3px;
    background-color: white;
    border-radius: 2px;
    transition: transform 0.3s, opacity 0.3s;
}

.sidebar-toggle.active {
    left: 300px;
}

.sidebar-toggle.active span:nth-child(1) {
    transform: rotate(45deg) translate(6px, 6px);
}

.sidebar-toggle.active span:nth-child(2) {
    opacity: 0;
}

.sidebar-toggle.active span:nth-child(3) {
    transform: rotate(-45deg) translate(6px, -6px);
}

/* Main content */
.main-content {
    margin-left: 280px;
    padding: 20px;
    transition: margin-left 0.3s ease;
}

.main-content.expanded {
    margin-left: 0;
}

.container {
    max-width: 800px;
    margin: 0 auto;
}

h1 {
    text-align: center;
    color: #2c3e50;
    margin-bottom: 30px;
    /* offset when sidebar is visible on larger screens */
    margin-left: 60px;
    margin-right: 60px;
}

.search-container {
    margin-bottom: 30px;
}

#searchInput {
    width: 100%;
    padding: 12px 20px;
    font-size: 16px;
    border: 2px solid #bdc3c7;
    border-radius: 8px;
    outline: none;
    transition: border-color 0.3s;
}

#searchInput:focus {
    border-color: #3498db;
}

.words-container {
    display: block;
}

.lesson-section {
    margin-bottom: 30px;
    scroll-margin-top: 80px;
}

.lesson-section h2 {
    margin: 0 0 12px 0;
    color: #34495e;
    font-size: 1.1rem;
}

.lesson-list {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: 16px;
}

.word-card {
    background-color: white;
    border-radius: 8px;
    padding: 20px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    transition: transform 0.2s, box-shadow 0.2s;
}

.word-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

.greek {
    font-size: 1.2em;
    color: #2c3e50;
    margin-bottom: 8px;
}

.russian {
    color: #7f8c8d;
}

.hidden {
    display: none;
}

/* Mobile styles */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-280px);
    }

    .sidebar.collapsed {
        transform: translateX(-280px);
    }

    .sidebar:not(.collapsed) {
        transform: translateX(0);
    }

    .sidebar-toggle {
        left: 20px;
    }

    .sidebar-toggle.active {
        left: 300px;
    }

    .main-content {
        margin-left: 0;
    }

    .main-content.expanded {
        margin-left: 0;
    }

    /* Overlay for mobile */
    .sidebar-overlay {
        display: none;
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background-color: rgba(0, 0, 0, 0.5);
        z-index: 998;
    }

    .sidebar-overlay.active {
        display: block;
    }
}