:root {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --accent-color: #f9e487;
    --secondary-color: #03dac6;
    --nav-bg: #1f1f1f;
    --card-bg: #1e1e1e;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: var(--font-family);
    margin: 0;
    padding: 0;
    line-height: 1.6;
}

#study-list {
    background-color: var(--nav-bg);
    padding: 2rem 1rem;
    text-align: center;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
}

#study-list a {
    color: var(--accent-color);
    text-decoration: none;
    font-size: 1rem;
    font-weight: bold;
    transition: color 0.3s ease;
}

#study-list a:hover {
    color: var(--secondary-color);
}

nav {
    background-color: var(--nav-bg);
    position: sticky;
    top: 0;
    z-index: 1000;
}

#ulid {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    overflow-x: auto;
}

.liclass a {
    display: block;
    color: var(--text-color);
    text-align: center;
    padding: 1rem 1.5rem;
    text-decoration: none;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.liclass a:hover {
    background-color: rgba(255, 255, 255, 0.1);
    color: var(--accent-color);
}

main {
    max-width: 800px;
    margin: 2rem auto;
    padding: 0 1rem;
}

section {
    margin-bottom: 3rem;
    padding: 2rem;
    background-color: var(--card-bg);
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
}

h1, h2, h3 {
    color: var(--accent-color);
}

.santa {
    border-radius: 50%;
    width: 250px;
    height: 250px;
    object-fit: cover;
    display: block;
    margin: 1.5rem auto;
    border: 4px solid var(--accent-color);
    transition: transform 0.5s ease;
}

.santa:hover {
    transform: scale(1.05);
}

.claus {
    width: 60px;
    height: 60px;
    opacity: 0.5;
    transition: all 0.3s ease;
    cursor: pointer;
}

.claus:hover {
    width: 90px;
    height: 90px;
    opacity: 1.0;
}

.rotate {
    width: 100px;
    height: 100px;
    display: block;
    margin: 2rem auto;
    transition: all 1.5s ease-in-out;
}

.rotate:hover {
    width: 200px;
    height: 200px;
    transform: rotate(360deg);
}

.contact-icons {
    display: flex;
    justify-content: center;
    gap: 2rem;
    padding: 1rem 0;
}

.contact-icon {
    width: 50px;
    height: 50px;
    transition: transform 0.3s ease, filter 0.3s ease;
    filter: grayscale(100%) brightness(1.2);
}

.contact-icon:hover {
    transform: translateY(-5px) scale(1.1);
    filter: grayscale(0%) brightness(1);
}

.contact-list {
    list-style: none;
    padding: 0;
}

.contact-list li {
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
}

button {
    background-color: var(--accent-color);
    color: var(--bg-color);
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
    transition: background-color 0.3s ease;
    margin-left: 0.5rem;
}

button:hover {
    background-color: var(--secondary-color);
}

footer {
    text-align: center;
    padding: 2rem;
    font-size: 0.9rem;
    opacity: 0.7;
}

hr {
    border: 0;
    height: 1px;
    background-image: linear-gradient(to right, rgba(0, 0, 0, 0), rgba(255, 255, 255, 0.2), rgba(0, 0, 0, 0));
    margin: 2rem 0;
}