body {
    font-family: sans-serif;
    background: #111;
    color: #eee;
    margin: 0;
    padding: 20px;
}
h1 {
    text-align: center;
}
.filter {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-bottom: 20px;
}
.filter button {
    padding: 8px 14px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    background: #333;
    color: #eee;
    transition: background 0.3s;
}
.filter button.active,
.filter button:hover {
    background: #555;
}
.timeline {
    display: flex;
    flex-direction: column;
    gap: 20px;
    max-width: 600px;
    margin: auto;
    max-height: 100vh;
    height: 100%;
    overflow-y: scroll;
}
.event {
    padding: 15px;
    border-left: 3px solid;
    background: #222;
    border-radius: 5px;
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s, transform 0.6s;
    cursor: pointer;
}
.event.visible {
    opacity: 1;
    transform: translateY(0);
}
.year {
    font-weight: bold;
    font-size: 1.1em;
}
.title {
    font-size: 1.2em;
    margin: 5px 0;
}
.description {
    color: #ccc;
    display: none;
    margin-top: 8px;
}
.event.open .description {
    display: block;
}
/* 時代ごとの色分け */
.era-宇宙の始まり { border-color: #0ff; }
.era-太陽系誕生 { border-color: #0f0; }
.era-人類史 { border-color: #ffa500; }
.era-近代史 { border-color: #a0f; }