```css
@charset "UTF-8";

* {
    box-sizing: border-box;
}

html,
body {
    margin: 0;
    padding: 0;
    min-height: 100%;
}

body {
    background-color: #101217;
    color: #d8dce5;
    font-family:
        "Noto Sans JP",
        "Yu Gothic",
        "Meiryo",
        sans-serif;
}

.container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 40px 20px;
    text-align: center;
}

h1 {
    margin: 0 0 30px;
    font-size: clamp(1.1rem, 3vw, 1.8rem);
    font-weight: 400;
    letter-spacing: 0.05em;
}

.main-image {
    display: block;
    width: 100%;
    max-width: 800px;
    height: auto;
    border: 1px solid #303542;
}

.administrator {
    margin: 30px 0 0;
    font-size: 0.95rem;
    color: #8e96a8;
}

.administrator a {
    color: #aeb9d1;
    text-decoration: none;
    transition: color 0.2s ease;
}

.administrator a:hover {
    color: #ffffff;
    text-decoration: underline;
}
```