:root {
    --primary-color: #2563eb;
    --secondary-color: #1e40af;
    --text-color: #1f2937;
    --light-bg: #f3f4f6;
    --white: #ffffff;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-400: #9ca3af;
    --gray-500: #6b7280;
    --gray-600: #4b5563;
    --gray-700: #374151;
    --gray-800: #1f2937;
    --gray-900: #111827;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', sans-serif;
    line-height: 1.6;
    color: var(--text-color);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
}


/* Header Styles */
.header {
    background-color: var(--white);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 2rem;
    max-width: 1200px;
    margin: 0 auto;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-links a {
    text-decoration: none;
    color: var(--gray-700);
    font-weight: 500;
    transition: color 0.3s ease;
}

.nav-links a:hover {
    color: var(--primary-color);
}

/* Hero Section */
.hero {
    background-image: url('assets/sandiego.jpeg');
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    color: var(--white);
  
    /* 关键：让这一块正好一屏高，并用 Flexbox 居中 */
    height: 100vh;
    display: flex;
    justify-content: center; /* 水平居中 */
    align-items: center;     /* 垂直居中 */
  
    /* 去掉原来的上下 padding */
    padding: 0 2rem;
    position: relative;
  }
  
  .hero-content {
    max-width: 1200px;
    text-align: center;
    /* margin:0 auto;  可以删掉，这里 Flexbox 已经帮你水平居中了 */
    position: relative;
    z-index: 1;
  }
  
  /* 字体大小、间距等保持不变 */
  .hero h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 1rem;
  }
  
  .hero h2 {
    font-size: 2rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
  }
  

.hero-subtitle {
    font-size: 1.25rem;
    margin-bottom: 2rem;
}

.cta-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
}

.cta-primary, .cta-secondary, .cta-third {
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    font-weight: 500;
    text-decoration: none;
    transition: all 0.3s ease;
}

.cta-primary {
    background-color: var(--white);
    color: var(--primary-color);
}

.cta-secondary {
    background-color: transparent;
    color: var(--white);
    border: 2px solid var(--white);
}

.cta-primary:hover {
    background-color: var(--gray-100);
    transform: translateY(-2px);
}

.cta-secondary:hover {
    background-color: var(--white);
    color: var(--primary-color);
    transform: translateY(-2px);
}


/* Section Styles */
.section {
    padding: 5rem 0;
}

.section h2 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 3rem;
    text-align: center;
}

.bg-light {
    background-color: var(--light-bg);
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 2rem;
    margin-top: 3rem;
}

.stat-item {
    text-align: center;
    padding: 2rem;
    background-color: var(--white);
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.stat-item h3 {
    font-size: 2rem;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

/* Topics Grid */
.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(275px, 1fr));
    gap: 2rem;
}

.topic-card {
    background-color: var(--white);
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.topic-card h3 {
    color: var(--primary-color);
    margin-bottom: 1rem;
}

/* Organizers Grid */
.organizers-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
}

.organizer-card {
    background-color: var(--white);
    padding: 1.5rem;
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    text-align: center;
    transition: transform 0.3s ease;
}

.organizer-card:hover {
    transform: translateY(-5px);
}

.profile-image {
    width: 120px;
    height: 120px;
    margin: 0 auto 1rem;
    border-radius: 50%;
    overflow: hidden;
    border: 3px solid var(--primary-color);
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.profile-img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.3s ease;
}

.organizer-card:hover .profile-img {
    transform: scale(1.05);
}

.organizer-card h3 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.affiliation {
    color: var(--gray-600);
    margin-bottom: 0.5rem;
    font-size: 0.8rem;
}

.affiliation-speaker {
    color: var(--gray-600);
    margin-bottom: 0.5rem;
    font-size: 1.0rem;
}

.role {
    color: var(--gray-500);
    font-size: 0.9rem;
}

/* Speakers Grid */
.speakers-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
}

.speaker-card {
    background-color: var(--white);
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    text-align: center;
}

.speaker-card h3 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

/* Schedule Timeline */
.schedule-timeline {
    max-width: 800px;
    margin: 0 auto;
}

.timeline-item {
    display: flex;
    align-items: center;
    margin-bottom: 1.5rem;
    background-color: var(--white);
    padding: 1.5rem;
    border-radius: 0.5rem;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.time {
    font-weight: 600;
    color: var(--primary-color);
    min-width: 100px;
}

.event {
    margin-left: 1rem;
}

/* Submission Section */
.submission-info {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.dates-list {
    list-style: none;
}

.dates-list li {
    margin-bottom: 1rem;
}

/* Footer */
.footer {
    background-color: var(--gray-900);
    color: var(--white);
    padding: 4rem 0 2rem;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-section h3 {
    color: var(--white);
    margin-bottom: 1rem;
}

.social-links {
    display: flex;
    gap: 1rem;
}

.social-link {
    color: var(--white);
    text-decoration: none;
    transition: color 0.3s ease;
}

.social-link:hover {
    color: var(--primary-color);
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid var(--gray-700);
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        gap: 1rem;
    }

    .nav-links {
        flex-direction: column;
        text-align: center;
        gap: 1rem;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .hero h2 {
        font-size: 1.5rem;
    }

    .section h2 {
        font-size: 2rem;
    }

    .cta-buttons {
        flex-direction: column;
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.section {
    animation: fadeIn 0.6s ease-out;
} 


/* Schedule Timeline */
.schedule-timeline {
    max-width: 800px;
    margin: 0 auto;
}

.timeline-item {
    display: flex;
    align-items: center;
    margin-bottom: 1.5rem;
    background-color: var(--white);
    padding: 1.5rem;
    border-radius: 0.5rem;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.time {
    font-weight: 600;
    color: var(--primary-color);
    min-width: 100px;
}

.event {
    margin-left: 1rem;
}

/* Submission Section */
.submission-info {
    display: grid;
    grid-template-columns: 1fr;
    gap: 2rem;
}

.dates-list {
    list-style: none;
}

.dates-list li {
    margin-bottom: 1rem;
}

.submission-guidelines-list {
    padding-left: 1.2em;
    margin-left: 0;
    list-style-position: inside;
    text-indent: -1.2em;
}

/* Footer */
.footer {
    background-color: var(--gray-900);
    color: var(--white);
    padding: 4rem 0 2rem;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-section h3 {
    color: var(--white);
    margin-bottom: 1rem;
}

.social-links {
    display: flex;
    gap: 1rem;
}

.social-link {
    color: var(--white);
    text-decoration: none;
    transition: color 0.3s ease;
}

.social-link:hover {
    color: var(--primary-color);
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid var(--gray-700);
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        padding: 1rem;
    }

    .nav-links {
        flex-direction: column;
        text-align: center;
        gap: 1rem;
        width: 100%;
        padding: 1rem 0;
        display: none; /* Hidden by default on mobile */
    }

    .nav-links.active {
        display: flex; /* Show when active */
    }

    .nav-links li {
        width: 100%;
    }

    .nav-links a {
        display: block;
        padding: 0.5rem;
        width: 100%;
    }

    .hero {
        padding: 6rem 1rem 4rem;
    }

    .hero h1 {
        font-size: 1.75rem;
        line-height: 1.3;
    }

    .hero h2 {
        font-size: 1.5rem;
    }

    .hero-subtitle {
        font-size: 1.1rem;
    }

    .section h2 {
        font-size: 2rem;
    }

    .cta-buttons {
        flex-direction: column;
        gap: 1rem;
    }

    .container {
        padding: 0 1rem;
    }

    .topics-grid,
    .organizers-grid,
    .speakers-grid {
        grid-template-columns: 1fr;
    }

    .topics-grid {
        grid-template-columns: 1fr;
        padding: 0 1rem;
    }
    
    .topic-card {
        padding: 2rem;
    }

    .organizers-grid {
        grid-template-columns: 1fr;
        padding: 0 1rem;
    }
}

/* Add hamburger menu styles */
.menu-toggle {
    display: none;
    cursor: pointer;
    padding: 0.5rem;
}

@media (max-width: 768px) {
    .menu-toggle {
        display: block;
        position: absolute;
        right: 1rem;
        top: 1rem;
    }

    .menu-toggle span {
        display: block;
        width: 25px;
        height: 3px;
        background-color: var(--primary-color);
        margin: 5px 0;
        transition: all 0.3s ease;
    }

    .menu-toggle.active span:nth-child(1) {
        transform: rotate(45deg) translate(5px, 5px);
    }

    .menu-toggle.active span:nth-child(2) {
        opacity: 0;
    }

    .menu-toggle.active span:nth-child(3) {
        transform: rotate(-45deg) translate(7px, -6px);
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.section {
    animation: fadeIn 0.6s ease-out;
}

/* Global Link Styles */
a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
}

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

/* Keep specific link styles that need to be different */
.nav-links a {
    color: var(--gray-700);
    font-weight: 500;
}

.nav-links a:hover {
    color: var(--primary-color);
}

.cta-primary, .cta-secondary {
    text-decoration: none;
}

.cta-primary {
    color: var(--primary-color);
}

.cta-secondary {
    color: var(--white);
}

.social-link {
    color: var(--white);
}

.social-link:hover {
    color: var(--primary-color);
}

/* Go to Top Button */
#go-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: var(--white);
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s ease;
    z-index: 1000;
}

#go-to-top.show {
    opacity: 1;
    visibility: visible;
}

#go-to-top:hover {
    background-color: var(--secondary-color);
    transform: translateY(-3px);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.3);
}

.hero h2 a {
    color: var(--white);
    text-decoration: none;
    transition: color 0.3s;
}

.hero-caption {
    position: absolute;
    right: 2.5rem;
    bottom: 0.2rem;
    display: flex;
    align-items: center;
    gap: 0.5em;
    background: rgba(0,0,0,0.35);
    color: #fff;
    padding: 0.5em 1.2em;
    border-radius: 1.2em;
    font-size: 0.8em;
    z-index: 2;
    box-shadow: 0 2px 8px rgba(0,0,0,0.08);
}

.hero-caption i {
    color: var(--primary-color-alt);
    font-size: 1.2em;
    margin-right: 0.4em;
}

.hero-caption a {
    color: #fff;
    transition: color 0.2s;
}

.hero-caption a:hover {
    color: var(--primary-color-alt);
}

.hero a:hover,
.hero .cta-primary:hover,
.hero .cta-secondary:hover {
    color: var(--primary-color-alt) !important;
    border-color: var(--primary-color-alt) !important;
}

.flex-bullet {
    display: flex;
    align-items: center;
    gap: 4em;
    list-style-type: disc;
    list-style-position: inside;
    position: relative;
}
.important-dates-table {
    width: 50%;
    border-collapse: collapse;
    margin: 0 auto 2em auto;
    table-layout: fixed;
}
.important-dates-table td {
    padding: 0.5em 0.8em;
    vertical-align: middle;
    border: none;
    font-size: 1em;
}
.important-dates-table td.event-col {
    width: 200px;
}
.important-dates-table td.date-col {
    width: 260px;
}
.important-dates-table td.countdown-col {
    width: 170px;
    text-align: left;
    padding-left: 0.8em;
}
.countdown-clock {
    font-size: 0.9em;
    color: var(--primary-color-alt);
    font-weight: 600;
    display: inline-block;
    text-align: left;
    white-space: nowrap;
}

.important-dates-table tr:not(:last-child) td {
    border-bottom: 1px solid #e0e0e0;
}
.important-dates-table tr:first-child td {
    border-top: 1px solid #e0e0e0;
}
.important-dates-table tr:last-child td {
    border-bottom: 1px solid #e0e0e0;
}