body {
    font-family: 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
    background: linear-gradient(120deg, #f7fafd 0%, #e9eaf0 100%);
    color: #232d36;
    margin: 0;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.letter-container {
    background: #fff;
    max-width: 660px;
    margin: 5vw auto 4vw auto;
    padding: 2.8rem 2.2rem 2.8rem 2.2rem;
    border-radius: 18px;
    box-shadow: 0 8px 48px rgba(34,44,64,0.13);
    font-size: 1.18rem;
    line-height: 1.85;
    word-break: break-word;
    min-height: 340px;
    letter-spacing: 0.01em;
    color: #24292f;
    display: block;
}

.letter-container img,
.letter-container video,
.letter-container iframe {
    max-width: 100%;
    border-radius: 10px;
    margin: 1.7em 0;
    box-shadow: 0 2px 14px rgba(34,44,64,0.05);
}

.letter-container a {
    color: #2450a8;
    text-decoration: underline;
    word-break: break-all;
    transition: color 0.18s;
}

.letter-container a:hover {
    color: #1b355a;
    text-decoration: underline;
}

@media (max-width: 800px) {
    .letter-container {
        max-width: 96vw;
        padding: 1.3rem 4vw;
        font-size: 1.01rem;
        margin: 4vw 1vw 4vw 1vw;
    }
}

footer {
    text-align: center;
    color: #5c6672;
    padding-bottom: 2em;
    font-size: 0.97em;
    opacity: 0.65;
    margin-top: auto;
}