/* =========================================
   GENERAL STYLES
========================================= */
body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #ffffff;
    color: #00334d;
    margin: 0;
    padding: 0 60px;
    scroll-behavior: smooth;
}

h1, h2, h3 {
    color: #000;
}

p {
    line-height: 1.7;
}

/* =========================================
   CONTAINERS
========================================= */
.container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 20px;
    box-sizing: border-box;
}

.main-content {
    max-width: 1000px;
    margin: 20px auto;
    background-color: #e6f7ff;
    box-shadow: 0px 2px 10px rgba(0,0,0,0.2);
}

/* =========================================
   HEADER
========================================= */
header {
    background: linear-gradient(90deg, #006699 0%, #0099cc 100%);
    color: #fff;
    text-align: center;
    padding: 40px 20px;
}

/* =========================================
   NAVIGATION
========================================= */
nav {
    background-color: #004466;
    text-align: center;
    padding: 12px 20px;
    position: sticky;
    top: 0;
    z-index: 1000;
}

/* Desktop links */
nav .container {
    display: flex;
    justify-content: center; 
    align-items: center;
    position: relative;
}

nav a {
    color: #fff;
    margin: 0 20px;
    text-decoration: none;
    font-weight: bold;
    font-size: 1em;
    transition: all 0.3s ease;
}

nav a:hover,
nav a:focus {
    color: #00ccff;
    text-decoration: underline;
}

/* Hamburger menu */
.hamburger {
    display: none;
    font-size: 28px;
    color: #fff;
    cursor: pointer;
    position: absolute;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
}

/* Hamburger active state */
.hamburger.active {
    content: "✖"; /* fallback, though we'll change innerText via JS */
    font-size: 28px;
}

/* Desktop navigation flex */
.nav-links {
    display: flex;
    gap: 25px;
}

/* =========================================
   SECTIONS
========================================= */
section {
    padding: 60px 0;
    text-align: justify;
}

section img,
section video {
    display: block;
    max-width: 100%;
    margin: 20px auto;
    box-shadow: 0px 5px 15px rgba(0,0,0,0.2);
}

/* =========================================
   LISTS
========================================= */
ul {
    list-style: none;
    padding-left: 0;
}

ul li {
    margin: 10px 0;
}

ul li a {
    text-decoration: none;
    color: #005580;
    font-weight: bold;
    transition: color 0.3s ease;
}

ul li a:hover,
ul li a:focus {
    color: #00ccff;
}

/* =========================================
   MODEL DIAGRAM
========================================= */
.model-diagram {
    max-width: 60%;
    margin: 20px auto;
}

/* =========================================
   RESULTS SECTION
========================================= */
.results-images {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 20px;
}

.results-images img {
    max-width: 90%;
}

.video-container {
    position: relative;
    width: 90%;
    max-width: 900px;
    margin: 20px auto;
    padding-bottom: 56.25%;
    height: 0;
}

.video-container iframe {
    position: absolute;
    inset: 0;
    width: 100%;
    height: 100%;
    border: 0;
}

/* =========================================
   MATERIALS
========================================= */
.materials-links {
    display: flex;
    justify-content: center;
    gap: 40px;
    flex-wrap: wrap;
    margin-top: 20px;
}

.materials-links img {
    width: 80px;
    height: 80px;
    object-fit: contain;
    transition: transform 0.3s ease;
    cursor: pointer;
}

.materials-links img:hover,
.materials-links img:focus {
    transform: scale(1.1);
}

.materials-links img:first-child,
.materials-links img:last-child {
    margin: 0; /* removed large left/right margin */
}

/* =========================================
   CITATION BOX
========================================= */
.citation-box {
    background-color: #f0faff;
    border: 1px solid #b3d9ff;
    padding: 20px;
    border-radius: 8px;
    font-family: "Courier New", monospace;
    font-size: 0.95em;
    white-space: pre-wrap;
    width: 100%;
    max-width: 1000px;
    margin: 20px auto;
    box-sizing: border-box;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

/* =========================================
   HIGHLIGHTS
========================================= */
.highlight {
    color: red;
    font-weight: bold;
}

/* =========================================
   FOOTER
========================================= */
footer {
    background-color: #004466;
    color: #fff;
    text-align: center;
    padding: 25px 10px;
    position: relative;
    border-top: 4px solid #00ccff; /* thin line at top */
}


/* =========================================
   RESPONSIVE DESIGN
========================================= */

/* --- Max-width 1024px (Tablet) --- */
@media (max-width: 1024px) {
    body { padding: 0 30px; }
    .container, .main-content { max-width: 95%; }
    .model-diagram { max-width: 75%; }

    h1 { font-size: 1.9em; }
    h2 { font-size: 1.5em; }
    h3 { font-size: 1.3em; }
    p  { font-size: 1.03em; }
}

/* --- Max-width 768px (Small Tablet / Mobile) --- */
@media (max-width: 768px) {
    body { padding: 0 15px; }

    /* Header & Sections */
    header { padding: 25px 10px; }
    section { padding: 35px 0; }
    footer { padding: 18px 10px; }

    /* Results */
    .results-images {
        flex-direction: column;
        gap: 10px;
    }

    /* Navigation */
    nav .container {
        padding: 0; /* remove side padding */
        justify-content: center; /* center links */
    }

    .hamburger {
        display: block;
    }

    .nav-links {
        display: none;
        flex-direction: column;
        width: 100%;
        margin-top: 50px;
        background-color: #004466;
        border-radius: 5px;
        padding: 10px 0;
        text-align: center;
    }

    .nav-links a {
        display: block;
        margin: 10px 0;
        color: #fff;
    }

    .nav-links.active {
        display: flex;
    }

    /* Materials */
    .materials-links img {
        width: 60px;
        height: 60px;
    }
}

/* --- Max-width 600px (Mobile) --- */
@media (max-width: 600px) {
    nav { padding: 10px; }
    nav a { font-size: 0.9em; }
    section { padding: 40px 0; }
    .model-diagram { max-width: 90%; }
    .materials-links { gap: 15px; }
    .citation-box { padding: 15px 20px; }

    h1 { font-size: 1.7em; }
    h2 { font-size: 1.35em; }
    h3 { font-size: 1.15em; }
    p  { font-size: 1em; }
}

/* --- Max-width 480px --- */
@media (max-width: 480px) {
    section { padding: 25px 0; }
    header  { padding: 18px 5px; }
    footer  { padding: 15px 5px; }
    .container, .main-content { padding: 0 10px; }
}

/* --- Max-width 420px (Extra Small Mobile) --- */
@media (max-width: 420px) {
    body { padding: 0 10px; }
    header { padding: 20px 5px; }

    h1 { font-size: 1.45em; }
    h2 { font-size: 1.2em; }
    h3 { font-size: 1.05em; }
    p  { font-size: 0.95em; }
    nav a { font-size: 0.82em; }

    .materials-links img { width: 50px; height: 50px; }
    .model-diagram { max-width: 100%; }
    footer { padding: 20px 5px; }
    .citation-box { padding: 12px 18px; }
}