style.css

:root {
    --radius: 12px;
    --shadow: 0 4px 24px rgba(0, 0, 0, 0.07);
    --nav-height: 56px;
    --primary: #181818;
    --sidebar-bg: #f7f8fa;
    --accent: #00c3ff;
    --bg: #fff;
}

body {
    margin: 0;
    font-family: "Inter", "Segoe UI", Arial, sans-serif;
    background: var(--bg);
    color: var(--primary);
    min-height: 100vh;
    line-height: 1.7;
    transition: background 0.6s;
}

/* === Era backgrounds === */
body.stone-age {
    --bg: #f7e7c2;
    background: radial-gradient(ellipse at 60% 20%, #fffbe6 40%, #f7e7c2 100%);
}
body.ancient {
    --bg: #f5f0e6;
    background: radial-gradient(ellipse at 50% 10%, #fffbe6 30%, #e4d6b7 100%);
}
body.industrial {
    --bg: #e6ecf5;
    background: linear-gradient(120deg, #e6ecf5 60%, #b7c4d6 100%);
}
body.digital {
    --bg: #f7faff;
    background: radial-gradient(ellipse at 70% 10%, #e6f4ff 30%, #c2e0ff 100%);
}
body.future {
    --bg: #f9f5ff;
    background: linear-gradient(120deg, #f9f5ff 60%, #e6e0ff 100%);
}

/* === Navigation === */
header nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: var(--sidebar-bg);
    padding: 0 2vw;
    height: var(--nav-height);
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 10;
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--accent);
    text-decoration: none;
    letter-spacing: 1px;
}

header nav ul {
    display: flex;
    gap: 1.2rem;
    list-style: none;
    margin: 0;
    padding: 0;
}

header nav ul li a {
    color: var(--primary);
    text-decoration: none;
    font-weight: 500;
    padding: 0.3rem 0.7rem;
    border-radius: var(--radius);
    transition:
        background 0.2s,
        color 0.2s;
}
header nav ul li a.active,
header nav ul li a:hover,
.era-link:hover {
    background: var(--accent);
    color: #fff;
}

main {
    max-width: 800px;
    margin: 2.5rem auto 2rem auto;
    padding: 0 1.2rem;
    position: relative;
}

.intro {
    text-align: center;
    margin-top: 2rem;
}

.era-grid {
    display: flex;
    flex-wrap: wrap;
    gap: 1.2rem;
    justify-content: center;
    margin-top: 2.5rem;
}
.era-link {
    display: inline-block;
    background: var(--sidebar-bg);
    color: var(--primary);
    font-size: 1.1rem;
    font-weight: 600;
    padding: 1.2rem 2.2rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    text-decoration: none;
    transition:
        background 0.2s,
        color 0.2s,
        transform 0.2s;
}
.era-link:hover {
    background: var(--accent);
    color: #fff;
    transform: scale(1.06) translateY(-2px);
}

h1,
h2,
h3 {
    font-family: "Inter", "Segoe UI", Arial, sans-serif;
    color: var(--accent);
    margin-top: 1.5em;
    margin-bottom: 0.5em;
}
h1 {
    font-size: 2.3rem;
}
h2 {
    font-size: 1.4rem;
}
h3 {
    font-size: 1.1rem;
    color: #7e5e2e;
}

.interactives {
    display: flex;
    flex-wrap: wrap;
    gap: 2.2rem;
    margin: 2.2rem 0;
    justify-content: space-between;
}
.interactives > div {
    flex: 1 1 260px;
    background: rgba(255, 255, 255, 0.9);
    border-radius: var(--radius);
    box-shadow: 0 2px 12px #0001;
    padding: 1.1rem 1rem 1.2rem 1rem;
    margin-bottom: 1rem;
    min-width: 220px;
}

blockquote {
    background: #fffbe6;
    border-left: 4px solid #ffe066;
    padding: 0.7em 1.2em;
    border-radius: 0 12px 12px 0;
    color: #7e5e2e;
    margin: 2em 0;
    font-style: italic;
}

.era-nav {
    margin: 2.5em 0 0 0;
    text-align: right;
}
.era-nav a {
    color: var(--accent);
    text-decoration: none;
    font-weight: 600;
    font-size: 1.1em;
    border-bottom: 1px solid #00c3ff55;
    transition: color 0.2s;
}
.era-nav a:hover {
    color: #7e5e2e;
}

footer {
    text-align: center;
    color: #aaa;
    font-size: 1rem;
    margin: 3rem 0 1rem 0;
}

button,
input[type="text"] {
    border-radius: 6px;
    border: 1px solid #e0e0e0;
    padding: 0.4em 0.8em;
    font-size: 1em;
    margin: 0.2em 0.2em 0.2em 0;
    background: #fff;
    transition:
        background 0.2s,
        border 0.2s;
}
button:hover,
input[type="text"]:focus {
    background: #e6f4ff;
    border-color: var(--accent);
}

@media (max-width: 700px) {
    main {
        max-width: 98vw;
    }
    .interactives {
        flex-direction: column;
    }
}