:root {
    --card-bg: rgba(255, 255, 255, 0.55);
    --text-primary: #000000;
    --text-secondary: #333333;
    --gradient-start: #007aff;
    --gradient-end: #00c6ff;
    --gradient-red-start: #ff4d4d;
    --gradient-red-end: #ff8c00;
    --border-color: rgba(255, 255, 255, 0.2);
    --platform-card-bg: rgba(255, 255, 255, 0.7);
    --platform-card-hover-bg: rgba(255, 255, 255, 0.9);
    --error-color: #d93025;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
    line-height: 1.6;
    margin: 0;
    padding: 2rem 1rem;
    color: var(--text-primary);
    -webkit-font-smoothing: antialiased;

    background-color: #f0f2f5;
    position: relative;
    overflow-x: hidden;
}

body::before, body::after {
    content: '';
    position: absolute;
    z-index: -1;
    filter: blur(100px);
    -webkit-filter: blur(100px);
}

body::before {
    width: 400px;
    height: 400px;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    border-radius: 50%;
    left: -150px;
    top: -150px;
    opacity: 0.5;
}

body::after {
    width: 500px;
    height: 500px;
    background: linear-gradient(135deg, #ff8c00, #ff0080);
    border-radius: 50%;
    right: -200px;
    bottom: -200px;
    opacity: 0.4;
}

header {
    padding: 1rem 1rem 2rem;
    text-align: center;
}

header h1 {
    font-size: 3rem;
    font-weight: 800;
    margin: 0 0 0.5rem;
    letter-spacing: -0.02em;
}

header p {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin: 0;
}

main {
    max-width: 720px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.card {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--border-color);
    padding: 2rem;
    border-radius: 24px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
}

.card h2 {
    font-size: 1.75rem;
    font-weight: 700;
    margin-top: 0;
    margin-bottom: 0.75rem;
}

.card p {
    color: var(--text-secondary);
    margin-top: 0;
    margin-bottom: 1.5rem;
}

.jump-container {
    display: flex;
    gap: 0.75rem;
}

#jump-input {
    flex-grow: 1;
    padding: 12px 16px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    background-color: rgba(255, 255, 255, 0.7);
    font-size: 1rem;
    outline: none;
    transition: all 0.3s ease;
}

#jump-input:focus {
    background-color: #fff;
    border-color: var(--gradient-start);
    box-shadow: 0 0 0 3px rgba(0, 122, 255, 0.2);
}

#jump-button {
    flex-shrink: 0;
    width: auto;
}

.error-message {
    color: var(--error-color);
    font-weight: 500;
    margin-top: 1rem;
    display: none; /* Hidden by default */
}

.platform-cards {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
    align-items: start;
}

.platform-card {
    background: var(--platform-card-bg);
    border-radius: 16px;
    padding: 1.5rem 1rem;
    text-align: center;
    color: var(--text-primary);
    transition: background 0.3s ease, transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid var(--border-color);
    cursor: pointer;
}

.platform-card:hover {
    background: var(--platform-card-hover-bg);
    transform: translateY(-4px);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.08);
}

.platform-header h3 {
    margin: 0 0 0.25rem;
    font-size: 1.2rem;
    font-weight: 600;
}

.platform-header span {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.platform-content {
    max-height: 0;
    opacity: 0;
    transition: max-height 0.4s ease-out, opacity 0.3s ease-out, margin-top 0.4s ease-out;
    overflow: hidden;
    box-sizing: border-box;
    padding: 0 0.5rem 1rem;
}

.platform-description {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin: 0 0 1rem 0;
    padding: 0;
}

.platform-card.expanded .platform-content {
    max-height: 300px;
    opacity: 1;
    margin-top: 1.5rem;
}

.platform-card.expanded {
    background: var(--card-bg);
    box-shadow: inset 0 0 0 2px var(--gradient-start);
    transform: translateY(0);
}

.button {
    display: inline-block;
    background: linear-gradient(135deg, var(--gradient-start) 0%, var(--gradient-end) 100%);
    color: #ffffff;
    padding: 10px 20px;
    font-size: 0.9rem;
    font-weight: 600;
    text-decoration: none;
    border-radius: 999px;
    box-shadow: 0 4px 10px rgba(0, 122, 255, 0.3);
    transition: all 0.3s ease;
    border: none;
    cursor: pointer;
    width: 100%;
    box-sizing: border-box;
}

.button + .button {
    margin-top: 0.75rem;
}

.button-continue {
    background: linear-gradient(135deg, var(--gradient-red-start) 0%, var(--gradient-red-end) 100%);
    box-shadow: 0 4px 10px rgba(255, 77, 77, 0.3);
}

.button:hover {
    transform: scale(1.03);
    box-shadow: 0 6px 15px rgba(0, 122, 255, 0.4);
}

.button-continue:hover {
    box-shadow: 0 6px 15px rgba(255, 77, 77, 0.4);
}

.tutorial-content {
    max-height: 0;
    opacity: 0;
    overflow: hidden;
    transition: max-height 0.5s ease-in-out, opacity 0.5s ease-in-out, margin-top 0.5s ease-in-out;
    margin-top: 0;
}

.tutorial-content.expanded {
    max-height: 2000px;
    opacity: 1;
    margin-top: 1.5rem;
}

img {
    max-width: 100%;
    height: auto;
    border-radius: 16px;
    display: block;
    margin: 1rem auto 0;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

footer {
    text-align: center;
    padding: 3rem 1rem 2rem;
    color: #666;
    font-size: 0.875rem;
    background: transparent;
}