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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #87CEEB, #E0F6FF);
    color: #333;
    line-height: 1.6;
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    background: rgba(255, 255, 255, 0.95);
    border-radius: 15px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    overflow: hidden;
 
}

header {
    background: linear-gradient(135deg, #4A90E2, #67B26F);
    color: white;
    padding: 30px;
    text-align: center;
}

h1 {
    font-size: 2.5em;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.subtitle {
    font-size: 1.2em;
    opacity: 0.9;
}

/* ИСПРАВЛЕННЫЕ СТИЛИ ДЛЯ ОСНОВНОЙ НАВИГАЦИИ */
.nav-buttons {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 15px;
    padding: 25px 20px;
    background: rgba(255, 255, 255, 0.9);
    border-bottom: 1px solid rgba(106, 176, 238, 0.2);
}

/* Стили для ссылок-кнопок в основной навигации */
.nav-buttons a {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 14px 24px;
    background: linear-gradient(135deg, #4A90E2, #67B26F);
    color: white;
    border: none;
    border-radius: 30px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 12px rgba(74, 144, 226, 0.3);
    flex: 1;
    min-width: 140px;
    max-width: 200px;
    text-align: center;
    font-size: 1em;
    text-decoration: none;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    position: relative;
    overflow: hidden;
}

/* Состояния ссылок в основной навигации */
.nav-buttons a:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 20px rgba(74, 144, 226, 0.4);
    background: linear-gradient(135deg, #3a80d2, #57a25f);
    text-decoration: none;
}

.nav-buttons a:active {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(74, 144, 226, 0.3);
    text-decoration: none;
}

.nav-buttons a:visited {
    color: white;
    text-decoration: none;
}

.nav-buttons a:focus {
    outline: none;
    box-shadow: 0 0 0 3px rgba(255, 255, 255, 0.5), 0 4px 12px rgba(74, 144, 226, 0.3);
    text-decoration: none;
}

/* Эффект свечения для активной кнопки */
@keyframes buttonGlow {
    0% { box-shadow: 0 4px 12px rgba(74, 144, 226, 0.3), 0 0 0 0 rgba(74, 144, 226, 0.2); }
    70% { box-shadow: 0 4px 20px rgba(74, 144, 226, 0.5), 0 0 0 10px rgba(74, 144, 226, 0); }
    100% { box-shadow: 0 4px 12px rgba(74, 144, 226, 0.3), 0 0 0 0 rgba(74, 144, 226, 0); }
}

.nav-buttons a.active {
    animation: buttonGlow 2s infinite;
    border: 2px solid rgba(255, 255, 255, 0.5);
}

/* Градиентная рамка при наведении */
.nav-buttons a::before {
    content: '';
    position: absolute;
    top: -2px;
    left: -2px;
    right: -2px;
    bottom: -2px;
    background: linear-gradient(135deg, #4A90E2, #67B26F, #FF6B6B);
    border-radius: 32px;
    z-index: -1;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.nav-buttons a:hover::before {
    opacity: 0.8;
}

/* Анимация появления кнопок основной навигации */
.nav-buttons a {
    animation: fadeInUp 0.5s ease forwards;
    opacity: 0;
    transform: translateY(20px);
}

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

/* Задержка для каждой кнопки основной навигации */
.nav-buttons a:nth-child(1) { animation-delay: 0.1s; }
.nav-buttons a:nth-child(2) { animation-delay: 0.2s; }
.nav-buttons a:nth-child(3) { animation-delay: 0.3s; }
.nav-buttons a:nth-child(4) { animation-delay: 0.4s; }
.nav-buttons a:nth-child(5) { animation-delay: 0.5s; }
.nav-buttons a:nth-child(6) { animation-delay: 0.6s; }
.nav-buttons a:nth-child(7) { animation-delay: 0.7s; }
.nav-buttons a:nth-child(8) { animation-delay: 0.8s; }

.content {
    padding: 30px;
}

.intro, .conclusion {
    background: #f8f9fa;
    padding: 25px;
    border-radius: 10px;
    margin-bottom: 30px;
    border-left: 4px solid #4A90E2;
}

h2 {
    color: #2c3e50;
    margin-bottom: 15px;
    font-size: 1.5em;
}

.table-container {
    overflow-x: auto;
    margin: 30px 0;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

table {
    width: 100%;
    border-collapse: collapse;
    background: white;
    min-width: 800px;
}

th {
    background: linear-gradient(135deg, #4A90E2, #67B26F);
    color: white;
    padding: 15px;
    text-align: left;
    font-weight: 600;
    position: sticky;
    top: 0;
}

td {
    padding: 12px 15px;
    border-bottom: 1px solid #e1e1e1;
}

tr:nth-child(even) {
    background-color: #f8f9fa;
}

tr:hover {
    background-color: #e3f2fd;
    transition: background-color 0.3s ease;
}

.year-cell {
    font-weight: 600;
    color: #2c3e50;
}

.inventor-cell {
    color: #e74c3c;
    font-weight: 500;
}

.frequency-cell {
    color: #27ae60;
    font-weight: 500;
}

.features-cell {
    color: #8e44ad;
    font-size: 0.9em;
}

.fundamental-era {
    background-color: #fffacd;
}

.broadcast-era {
    background-color: #e6e6fa;
}

.digital-era {
    background-color: #ffe4e1;
}

.wireless-era {
    background-color: #d4edda;
}

.future-era {
    background-color: #e8f4f8;
}

.milestone {
    border-left: 4px solid #e74c3c;
}

.era-filter {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-bottom: 20px;
    justify-content: center;
}

.era-filter-btn {
    padding: 10px 20px;
    background: #f1f1f1;
    border: 1px solid #ddd;
    border-radius: 20px;
    cursor: pointer;
    transition: all 0.3s ease;
    font-weight: 500;
    text-decoration: none;
    color: #333;
    display: inline-block;
}

.era-filter-btn.active {
    background: linear-gradient(135deg, #4A90E2, #67B26F);
    color: white;
    border-color: #4A90E2;
    text-decoration: none;
}

.era-filter-btn:hover {
    background: #e0e0e0;
    text-decoration: none;
}

.era-filter-btn.active:hover {
    background: linear-gradient(135deg, #3a80d2, #57a25f);
    text-decoration: none;
}

.search-box {
    margin-bottom: 20px;
    display: flex;
    justify-content: center;
}

.search-box input {
    padding: 12px 20px;
    border: 1px solid #ddd;
    border-radius: 30px;
    width: 100%;
    max-width: 400px;
    font-size: 1em;
    transition: all 0.3s ease;
}

.search-box input:focus {
    outline: none;
    border-color: #4A90E2;
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.2);
}

/* ИСПРАВЛЕННЫЕ СТИЛИ ДЛЯ ФУТЕРА */
footer {
    background: linear-gradient(135deg, #2c3e50, #34495e);
    color: white;
    padding: 30px 20px;
    text-align: center;
    margin-top: 40px;
    border-radius: 0 0 15px 15px;
}

.footer-nav {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 15px;
    margin-bottom: 30px;
}

/* Стили для ссылок-кнопок в футере */
.footer-nav a {
    padding: 12px 24px;
    background: rgba(255, 255, 255, 0.15);
    color: white;
    border: 1px solid rgba(255, 255, 255, 0.3);
    border-radius: 25px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: center;
    min-width: 140px;
    text-decoration: none;
    display: inline-block;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

/* Состояния ссылок в футере */
.footer-nav a:hover {
    background: rgba(255, 255, 255, 0.25);
    transform: translateY(-3px);
    text-decoration: none;
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.3);
    border-color: rgba(255, 255, 255, 0.5);
}

.footer-nav a:active {
    transform: translateY(0);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
    text-decoration: none;
}

.footer-nav a:focus {
    outline: none;
    box-shadow: 0 0 0 2px rgba(255, 255, 255, 0.5);
    text-decoration: none;
}

.footer-nav a:visited {
    color: white;
    text-decoration: none;
}

/* Градиентная рамка для кнопок футера */
.footer-nav a::before {
    content: '';
    position: absolute;
    top: -1px;
    left: -1px;
    right: -1px;
    bottom: -1px;
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.3), rgba(255, 255, 255, 0.1));
    border-radius: 26px;
    z-index: -1;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.footer-nav a:hover::before {
    opacity: 1;
}

/* Анимация для кнопок футера */
.footer-nav a {
    opacity: 0;
    animation: fadeInFooter 0.6s ease forwards;
}

@keyframes fadeInFooter {
    to { opacity: 1; }
}

.footer-nav a:nth-child(1) { animation-delay: 0.1s; }
.footer-nav a:nth-child(2) { animation-delay: 0.2s; }
.footer-nav a:nth-child(3) { animation-delay: 0.3s; }
.footer-nav a:nth-child(4) { animation-delay: 0.4s; }
.footer-nav a:nth-child(5) { animation-delay: 0.5s; }

.copyright {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 15px;
    flex-wrap: wrap;
    margin-top: 20px;
    padding-top: 20px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
}

.copyright span {
    padding: 8px 16px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 20px;
    font-size: 0.9em;
    display: inline-block;
}

.copyright a {
    display: inline-block;
    margin-top: 10px;
}

.copyright img {
    border-radius: 4px;
    transition: transform 0.3s ease;
}

.copyright img:hover {
    transform: scale(1.05);
}

/* Дополнительные улучшения для кнопок */
.nav-buttons a i {
    margin-right: 8px;
    font-size: 1.1em;
}

/* Эффект пульсации для привлечения внимания */
@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

.nav-buttons a.highlight {
    animation: pulse 2s infinite;
    background: linear-gradient(135deg, #FF6B6B, #FF8E53);
}

.nav-buttons a.highlight:hover {
    background: linear-gradient(135deg, #FF5252, #FF7B42);
}

@media (max-width: 768px) {
    .container {
        margin: 10px;
    }
    
    h1 {
        font-size: 2em;
    }
    
    .content {
        padding: 15px;
    }
    
    th, td {
        padding: 8px 10px;
        font-size: 0.9em;
    }
    
    .nav-buttons {
        gap: 12px;
        padding: 20px 15px;
    }
    
    .nav-buttons a {
        padding: 12px 20px;
        font-size: 0.9em;
        min-width: 120px;
        max-width: 160px;
    }
    
    .footer-nav {
        gap: 12px;
        margin-bottom: 25px;
    }
    
    .footer-nav a {
        padding: 10px 18px;
        font-size: 0.9em;
        min-width: 120px;
    }
    
    .copyright {
        gap: 12px;
    }
    
    .copyright span {
        padding: 6px 12px;
        font-size: 0.85em;
    }
}

@media (max-width: 480px) {
    .nav-buttons {
        flex-direction: column;
        align-items: center;
        gap: 10px;
    }
    
    .nav-buttons a {
        max-width: 90%;
        width: 90%;
        min-width: auto;
        padding: 14px 20px;
    }
    
    .footer-nav {
        flex-direction: column;
        align-items: center;
        gap: 10px;
    }
    
    .footer-nav a {
        width: 80%;
        min-width: auto;
        padding: 12px 20px;
    }
    
    .era-filter {
        flex-direction: column;
        align-items: center;
    }
    
    .era-filter-btn {
        width: 80%;
        text-align: center;
    }
    
    .copyright {
        flex-direction: column;
        gap: 10px;
    }
    
    .copyright span {
        width: 80%;
        text-align: center;
    }
    
    footer {
        padding: 20px 15px;
    }
}

/* Дополнительные эффекты для всех ссылок */
a {
    transition: all 0.2s ease;
}

/* Плавный скролл для якорных ссылок */
html {
    scroll-behavior: smooth;
}

/* Улучшенная фокусировка для доступности */
a:focus-visible {
    outline: 2px solid #4A90E2;
    outline-offset: 2px;
    border-radius: 4px;
}

button:focus-visible {
    outline: 2px solid #4A90E2;
    outline-offset: 2px;
    border-radius: 4px;
}