body {
    font-family: 'Arial', 'Helvetica', 'Malgun Gothic', sans-serif;
    line-height: 1.65;
    background-color: #fff;
    color: #222;
    margin: 0;
    padding: 0 20px;
}
header {
    text-align: center;
    margin-bottom: 20px;
    padding-top: 40px;
}
header h1 {
    color: #000;
    font-size: 2.4rem;
    margin-bottom: 12px;
}
header p {
    font-size: 1.15em;
    color: #222;
    margin-bottom: 0;
}
main {
    max-width: 750px;
    margin: 0 auto;
    padding: 30px 0 0 0;
}
main h1, main h2 {
    color: #000;
    margin-top: 28px;
    margin-bottom: 14px;
}
ul {
    list-style-type: disc;
    padding-left: 22px;
    margin-bottom: 22px;
}
li {
    margin-bottom: 10px;
    font-size: 1.07rem;
    color: #000;
}
aside details {
    margin-top: 9px;
    color: #000;
}
details summary {
    cursor: pointer;
    font-weight: bold;
    color: #000;
    background: #f1f6ff;
    padding: 6px 12px;
    border-radius: 5px;
    transition: background 0.18s;
}
details[open] summary {
    background: #dbeafe;
}
mark {
    background-color: #fff18d;
    color: #000;
    border-radius: 3px;
    padding: 2px 4px;
}
table {
    border-collapse: collapse;
    width: 100%;
    margin: 22px 0;
    background-color: #f9fbff;
    box-shadow: 0 4px 12px rgba(55,98,230,0.05);
    color: #234183;
}
table th, table td {
    border: 1px solid #c1d4fa;
    padding: 11px;
    text-align: center;
    font-size: 1rem;
}
table th {
    background-color: #b9dbfa;
    font-weight: 600;
}
img {
    max-width: 96%;
    height: auto;
    display: block;
    margin: 18px auto;
    border-radius: 6px;
    box-shadow: 0 2px 9px rgba(55,98,230,0.08);
}
hr {
    border: none;
    border-top: 1px solid #bbb;
    margin: 32px 0 18px 0;
}

.button-wrapper {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin: 20px 0;
}
button.nav {
    margin: 0;
    padding: 11px 18px;
    border: none;
    border-radius: 8px;
    background-color: #87ceeb;
    color: #fff;
    font-size: 1rem;
    font-weight: bold;
    box-shadow: 0 2px 6px rgba(135, 206, 235, 0.16);
    cursor: pointer;
    transition: background-color 0.18s;
    display: inline-block;
}

button.nav:hover {
    background-color: #5dade2;
}
button.nav a {
    color: inherit;
    text-decoration: none;
    font-weight: bold;
}