/* CSS Variables and Global Reset */
:root {
    --iitb-blue: #004d99; /* Deep blue - primary color */
    --bentley-teal: #00a896; /* Teal/Secondary color */
    --accent-yellow: #ffc107; /* Pop of color for emphasis */
    --text-color-dark: #333;
    --text-color-light: #f8f9fa;
    --light-bg: #f5f8ff; /* Very light blue/grey */
    --dark-bg: #1c2b3a; /* Dark navy */
    --font-family: 'Poppins', sans-serif;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    line-height: 1.6;
    color: var(--text-color-dark);
    background-color: white;
    min-height: 100vh;
}

/* -------------------- Utility Classes & Layout -------------------- */
.container {
    width: 90%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px 0;
}

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

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

section {
    padding: 80px 0;
    overflow: hidden; /* For animations */
}

/* Headings */
.section-title {
    text-align: center;
    font-size: 2.5em;
    color: var(--iitb-blue);
    margin-bottom: 50px;
    font-weight: 700;
    position: relative;
}

.section-title::after {
    content: '';
    display: block;
    width: 80px;
    height: 4px;
    background: var(--bentley-teal);
    margin: 10px auto 0;
    border-radius: 2px;
}

.dark-bg .section-title {
    color: white;
}
.dark-bg .section-title::after {
    background: var(--accent-yellow);
}

/* -------------------- Header and Navigation -------------------- */
header {
    background: var(--iitb-blue);
    position: sticky;
    top: 0;
    z-index: 1000;
    padding: 15px 0;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

nav .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0;
}

.logo {
    font-size: 1.4em;
    font-weight: 700;
    color: white;
    text-decoration: none;
    letter-spacing: 0.5px;
    display: flex;
    align-items: center;
}

.nav-menu {
    list-style: none;
    display: flex;
    gap: 20px;
    /* transition: transform 0.3s ease-in-out; <-- Removed here, handled by media query and JS */
}

.nav-menu li a {
    color: white;
    text-decoration: none;
    padding: 8px 15px;
    border-radius: 5px;
    transition: background 0.3s, color 0.3s;
    font-weight: 400;
}

.nav-menu li a:hover {
    background: rgba(255, 255, 255, 0.15);
}

.cta-nav {
    background: var(--bentley-teal) !important;
    font-weight: 600 !important;
}

.cta-nav:hover {
    background: var(--accent-yellow) !important;
    color: var(--iitb-blue) !important;
}

.menu-toggle {
    display: none; /* Hide on desktop */
    background: none;
    border: none;
    color: white;
    font-size: 1.8em;
    cursor: pointer;
}

/* -------------------- Hero Section -------------------- */
#hero {
    background: linear-gradient(rgba(0, 50, 100, 0.8), rgba(0, 50, 100, 0.8)), url('assets/SIF_BG2.png') center/cover no-repeat;
    color: white;
    text-align: center;
    padding: 100px 20px;
}

#hero h1 {
    font-size: clamp(2em, 5vw, 4em);
    margin-bottom: 20px;
    font-weight: 700;
    line-height: 1.2;
}

.subtitle {
    font-size: 1.1em;
    font-weight: 300;
    letter-spacing: 2px;
    text-transform: uppercase;
    margin-bottom: 5px;
}

.org-info {
    font-size: clamp(1em, 2vw, 1.3em);
    font-weight: 400;
    opacity: 0.9;
}

.cta-button {
    display: inline-block;
    background: var(--bentley-teal);
    color: white;
    padding: 15px 35px;
    text-decoration: none;
    border-radius: 50px;
    font-weight: 600;
    letter-spacing: 1px;
    transition: background 0.3s, transform 0.3s, box-shadow 0.3s;
    box-shadow: 0 6px 15px rgba(0, 0, 0, 0.3);
}

.cta-button:hover {
    background: var(--accent-yellow);
    color: var(--iitb-blue);
    transform: translateY(-3px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.4);
}

/* -------------------- Details & Speakers -------------------- */
.grid-3 {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 30px;
    text-align: center;
}

.grid-4 {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 25px;
    text-align: center;
}

.key-detail, .speaker-card {
    background: white;
    padding: 25px;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.08);
    transition: transform 0.3s, box-shadow 0.3s;
    border-top: 5px solid var(--bentley-teal);
}

.key-detail:hover, .speaker-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.15);
}

.key-detail strong {
    display: block;
    font-size: 1.3em;
    color: var(--iitb-blue);
    margin-bottom: 8px;
    font-weight: 700;
}

.coordinators {
    margin-top: 50px;
    padding: 25px;
    background: #e9ecef;
    border-left: 5px solid var(--accent-yellow);
    border-radius: 8px;
    text-align: center;
}
.coordinators h3 {
    color: var(--iitb-blue);
    margin-bottom: 10px;
}

.speaker-card h4 {
    color: var(--bentley-teal);
    margin-top: 10px;
    font-size: 1.2em;
}

.speaker-card p {
    font-size: 0.9em;
    color: #666;
}

/* About Section */
.about-text {
    max-width: 900px;
    margin: 0 auto 20px;
    font-size: 1.05em;
    line-height: 1.7;
    text-align: justify;
}

/* Topics and Attendee Sections (Lists) */
.list-grid {
    column-count: 1;
    column-gap: 40px;
    list-style: none;
    padding-left: 0;
    max-width: 1000px;
    margin: 0 auto;
}

.list-grid li {
    padding: 10px 0;
    position: relative;
    padding-left: 30px;
    margin-bottom: 5px;
    border-bottom: 1px dashed rgba(255, 255, 255, 0.2); /* For dark-bg */
}

.list-grid li::before {
    content: '★'; /* Star icon */
    position: absolute;
    left: 0;
    color: var(--accent-yellow);
    font-weight: 600;
    font-size: 1.1em;
}

.light-bg .list-grid li {
    border-bottom: 1px dashed rgba(0, 0, 0, 0.1);
}
.light-bg .list-grid li::before {
    color: var(--bentley-teal);
}


/* -------------------- Registration Section -------------------- */
.register-section {
    background-color: var(--iitb-blue);
    color: white;
}

.reg-flex {
    display: flex;
    flex-direction: column;
    gap: 40px;
    align-items: flex-start;
}

.reg-details, .reg-payment {
    padding: 30px;
    border-radius: 10px;
    background: rgba(255, 255, 255, 0.1);
    width: 100%;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.reg-details h3, .reg-payment h3 {
    color: var(--accent-yellow);
    margin-bottom: 20px;
    font-size: 1.5em;
}

.fee-table {
    width: 100%;
    border-collapse: collapse;
    margin-bottom: 25px;
    font-size: 1.1em;
}

.fee-table th, .fee-table td {
    padding: 12px;
    border-bottom: 1px solid rgba(255, 255, 255, 0.3);
    text-align: left;
}

.fee-table th {
    color: white;
    font-weight: 600;
    background: rgba(0, 0, 0, 0.15);
}

.payment-info strong {
    display: block;
    margin-top: 15px;
    font-weight: 400;
}

.payment-info strong:first-child {
    margin-top: 0;
}

.account-note {
    font-size: 0.9em;
    opacity: 0.9;
    margin-top: 15px;
    line-height: 1.5;
}

.cta-group {
    margin-top: 25px;
    text-align: center;
}

.cta-button.primary {
    background: var(--bentley-teal);
}

.cta-button.secondary {
    background: var(--accent-yellow);
    color: var(--iitb-blue);
    font-weight: 700;
}

.qr-section {
    margin-top: 30px;
    text-align: center;
    padding-top: 20px;
    border-top: 1px solid rgba(255, 255, 255, 0.2);
}

.qr-code-img {
    max-width: 150px;
    height: auto;
    margin: 15px auto;
    border: 5px solid white;
    border-radius: 5px;
    display: block; /* Ensure it's centered */
}

.limit-note {
    text-align: center;
    margin-top: 50px;
    font-size: 1.2em;
    font-weight: 700;
    text-shadow: 0 0 5px rgba(0, 0, 0, 0.2);
}


/* -------------------- Footer -------------------- */
footer {
    background: var(--dark-bg);
    color: var(--text-color-light);
    text-align: center;
    padding: 20px 0;
    font-size: 0.9em;
}


/* -------------------- Media Queries (Mobile First) -------------------- */
@media (max-width: 767px) {
    /* Mobile Navigation Fixes */
    .menu-toggle {
        display: block;
    }

    .nav-menu {
        display: none; /* Keep hidden by default */
        flex-direction: column;
        position: absolute;
        top: 65px; /* Adjust based on header height */
        left: 0;
        width: 100%;
        background: var(--iitb-blue);
        padding: 10px 0;
        text-align: center;
        box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
        z-index: 999; /* Ensure it's above other content but below sticky header */
        /* Use JS to control 'display: flex' */
    }

    .nav-menu.open {
        display: flex;
    }
    
    .nav-menu li a {
        padding: 12px 15px;
        margin: 5px 20px;
        border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    }

    .nav-menu li:last-child a {
        border-bottom: none;
    }

    /* General Mobile Adjustments */
    section {
        padding: 60px 0;
    }
    
    .section-title {
        font-size: 2em;
        margin-bottom: 40px;
    }

    .list-grid {
        column-count: 1;
    }
    
    /* Registration adjustment */
    .reg-flex {
        gap: 30px;
    }
}

/* Tablet and Desktop */
@media (min-width: 768px) {
    .list-grid {
        column-count: 2;
    }
    
    .reg-flex {
        flex-direction: row;
        gap: 50px;
    }
    
    .reg-details, .reg-payment {
        width: 50%;
    }
    
    .grid-4 {
        grid-template-columns: repeat(4, 1fr);
    }
}