:root {
    --primary: #2868c7;
    --primary-dark: #1d4e8a;
    --bg: #f8fafc;
    --hint-bg: #f2f2f2;
    --success: #32a852;
    --danger: #d9534f;
    --radius: 10px;
    --shadow: 0 2px 12px 0 rgba(40,104,199,0.08);
}
html, body {
    margin: 0;
    padding: 0;
    background: var(--bg);
    color: #19233a;
    font-family: 'Segoe UI', Arial, sans-serif;
}
main {
    max-width: 520px;
    margin: 40px auto 0 auto;
    background: #fff;
    padding: 32px 24px 24px 24px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    text-align: left;
}
h1 {
    color: var(--primary);
    font-size: 2em;
    letter-spacing: 0.02em;
    margin-top: 0;
    margin-bottom: 12px;
}
h2 {
    font-size: 1.25em;
    margin: 28px 0 10px 0;
    color: #283851;
}
ul, ol {
    padding-left: 1.2em;
}
li {
    margin-bottom: 0.35em;
}
.btn, .back-link {
    display: block;
    width: 100%;
    margin: 32px 0 24px 0;
    padding: 17px 0;
    background: linear-gradient(90deg, var(--primary), var(--primary-dark));
    color: #fff;
    font-size: 1.25em;
    font-weight: 600;
    border: none;
    border-radius: var(--radius);
    box-shadow: 0 1px 6px 0 rgba(40,104,199,0.08);
    cursor: pointer;
    text-align: center;
    transition: background 0.15s;
    text-decoration: none;
}
.btn:hover, .back-link:hover {
    background: linear-gradient(90deg, var(--primary-dark), var(--primary));
}
.success-icon {
    font-size: 2.6em;
    color: var(--success);
    margin-bottom: 18px;
    text-align: center;
}
.success-message {
    font-size: 1.25em;
    color: var(--success);
    font-weight: 600;
    margin-bottom: 28px;
    text-align: center;
}
.hint {
    margin-top: 18px;
    background: var(--hint-bg);
    border-left: 4px solid var(--primary);
    padding: 14px 18px;
    border-radius: var(--radius);
    font-size: 1em;
}
img.demo-img {
    display: block;
    max-width: 100%;
    margin: 28px auto 0 auto;
    border-radius: var(--radius);
    border: 1.5px solid #e8eaf0;
    box-shadow: 0 2px 20px 0 rgba(40,104,199,0.06);
}
@media (max-width: 640px) {
    main { padding: 12px 5px; }
    h1 { font-size: 1.3em; }
}