/**
 * Modern Academic Website Styles
 * Dr. Yanshan Wang - University of Pittsburgh
 * Bootstrap 5.3.3 Compatible
 */

/* ========================================
   CSS Custom Properties (Variables)
   ======================================== */

:root {
    /* University of Pittsburgh Brand Colors */
    --pitt-blue: #003594;
    --pitt-blue-dark: #002570;
    --pitt-blue-light: #0047AB;
    --pitt-gold: #FFB81C;

    /* Semantic Colors */
    --primary: var(--pitt-blue);
    --primary-dark: var(--pitt-blue-dark);
    --primary-light: var(--pitt-blue-light);
    --accent: var(--pitt-gold);

    /* Neutral Palette */
    --gray-50: #f8f9fa;
    --gray-100: #e9ecef;
    --gray-200: #dee2e6;
    --gray-300: #ced4da;
    --gray-600: #6c757d;
    --gray-700: #495057;
    --gray-800: #343a40;
    --gray-900: #212529;
    --white: #ffffff;

    /* Typography */
    --font-primary: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
                    "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji",
                    "Segoe UI Emoji", "Segoe UI Symbol";
    --font-headings: Georgia, "Times New Roman", Times, serif;
    --font-monospace: "SF Mono", Monaco, "Cascadia Code", "Roboto Mono",
                      Consolas, "Courier New", monospace;

    /* Font Sizes */
    --font-size-base: 1rem;
    --font-size-sm: 0.875rem;
    --font-size-lg: 1.125rem;
    --line-height-base: 1.6;
    --line-height-heading: 1.2;

    /* Spacing */
    --section-padding-y: 4rem;
    --section-padding-x: 1rem;
    --card-padding: 1.5rem;
    --nav-height: 70px;

    /* Shadows */
    --shadow-sm: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.075);
    --shadow-md: 0 0.25rem 0.5rem rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 0.5rem 1rem rgba(0, 0, 0, 0.15);
    --shadow-hover: 0 0.75rem 1.5rem rgba(0, 0, 0, 0.2);

    /* Border Radius */
    --border-radius-sm: 0.25rem;
    --border-radius: 0.5rem;
    --border-radius-lg: 0.75rem;
    --border-radius-pill: 50rem;

    /* Transitions */
    --transition-base: all 0.3s ease-in-out;
    --transition-fast: all 0.15s ease-in-out;
    --transition-slow: all 0.5s ease-in-out;
}

/* Dark mode support (future-proofing) */
@media (prefers-color-scheme: dark) {
    :root {
        --gray-50: #212529;
        --gray-100: #343a40;
        --gray-900: #f8f9fa;
        --white: #1a1a1a;
    }
}

/* ========================================
   Base Styles
   ======================================== */

* {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-primary);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    color: var(--gray-900);
    background-color: var(--white);
    margin: 0;
    padding: 0;
    padding-top: var(--nav-height);
}

/* ========================================
   Typography
   ======================================== */

h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-headings);
    font-weight: 600;
    line-height: var(--line-height-heading);
    margin-top: 0;
    margin-bottom: 1rem;
    color: var(--gray-900);
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.75rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

.lead {
    font-size: var(--font-size-lg);
    font-weight: 300;
    line-height: 1.7;
}

p {
    margin-top: 0;
    margin-bottom: 1rem;
}

a {
    color: var(--primary);
    text-decoration: none;
    transition: var(--transition-fast);
}

a:hover {
    color: var(--primary-dark);
    text-decoration: underline;
}

strong, b {
    font-weight: 600;
}

em, i {
    font-style: italic;
}

/* ========================================
   Navigation
   ======================================== */

.navbar {
    backdrop-filter: blur(10px);
    background-color: rgba(255, 255, 255, 0.98) !important;
    box-shadow: var(--shadow-sm);
    transition: var(--transition-base);
    min-height: var(--nav-height);
}

.navbar-scrolled {
    box-shadow: var(--shadow-md);
}

.navbar-brand img {
    transition: var(--transition-fast);
    height: 50px;
    width: auto;
}

.navbar-brand img:hover {
    opacity: 0.9;
}

.nav-link {
    font-weight: 500;
    color: var(--gray-800);
    padding: 0.5rem 1rem !important;
    transition: var(--transition-fast);
    position: relative;
}

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

.nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    width: 0;
    height: 2px;
    background-color: var(--primary);
    transition: var(--transition-base);
    transform: translateX(-50%);
}

.nav-link:hover::after {
    width: 80%;
}

.dropdown-menu {
    border: none;
    box-shadow: var(--shadow-lg);
    border-radius: var(--border-radius);
    margin-top: 0.5rem;
    padding: 0.5rem 0;
}

.dropdown-item {
    padding: 0.5rem 1.5rem;
    transition: var(--transition-fast);
}

.dropdown-item:hover {
    background-color: var(--gray-50);
    color: var(--primary);
}

/* ========================================
   Layout Components
   ======================================== */

.hero-section {
    background: linear-gradient(135deg, var(--gray-50) 0%, var(--white) 100%);
    padding: var(--section-padding-y) var(--section-padding-x);
    margin-top: 0;
}

section {
    padding: var(--section-padding-y) var(--section-padding-x);
}

.section-alt {
    background-color: var(--gray-50);
}

/* ========================================
   Cards
   ======================================== */

.card {
    border: none;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-sm);
    transition: var(--transition-base);
    margin-bottom: 1.5rem;
    overflow: hidden;
}

.card:hover {
    box-shadow: var(--shadow-hover);
    transform: translateY(-4px);
}

.card-title {
    color: var(--primary);
    font-weight: 600;
    margin-bottom: 1rem;
}

.card-body {
    padding: var(--card-padding);
}

.card-header {
    background-color: var(--gray-50);
    border-bottom: 2px solid var(--primary);
    padding: 1rem var(--card-padding);
    font-weight: 600;
}

/* ========================================
   Buttons
   ======================================== */

.btn {
    border-radius: var(--border-radius);
    font-weight: 500;
    padding: 0.5rem 1.25rem;
    transition: var(--transition-base);
    border: none;
}

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

.btn-primary:hover {
    background-color: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn-outline-primary {
    border: 2px solid var(--primary);
    color: var(--primary);
    background-color: transparent;
}

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

/* ========================================
   Badges
   ======================================== */

.badge {
    border-radius: var(--border-radius-sm);
    padding: 0.35em 0.65em;
    font-weight: 500;
    font-size: 0.875em;
}

.badge-warning {
    background-color: var(--pitt-gold);
    color: var(--gray-900);
}

/* ========================================
   Images
   ======================================== */

img {
    max-width: 100%;
    height: auto;
}

.rounded {
    border-radius: var(--border-radius);
}

.shadow-sm {
    box-shadow: var(--shadow-sm);
}

/* Profile image */
.profile-image {
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-md);
    transition: var(--transition-base);
}

.profile-image:hover {
    box-shadow: var(--shadow-lg);
    transform: scale(1.02);
}

/* ========================================
   Lists
   ======================================== */

ul, ol {
    padding-left: 1.5rem;
    margin-bottom: 1rem;
}

.list-unstyled {
    padding-left: 0;
    list-style: none;
}

.list-unstyled li {
    margin-bottom: 0.75rem;
}

/* ========================================
   Publications & Content Lists
   ======================================== */

.publication-item {
    padding: 1rem 0;
    border-bottom: 1px solid var(--gray-200);
    transition: var(--transition-fast);
}

.publication-item:last-child {
    border-bottom: none;
}

.publication-item:hover {
    background-color: var(--gray-50);
    padding-left: 1rem;
    margin-left: -1rem;
    padding-right: 1rem;
    margin-right: -1rem;
    border-radius: var(--border-radius-sm);
}

/* ========================================
   Social Links
   ======================================== */

.social-links a {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    transition: var(--transition-fast);
}

.social-links a:hover {
    transform: translateX(4px);
}

/* ========================================
   Footer
   ======================================== */

footer {
    background-color: var(--gray-800);
    color: var(--gray-300);
    padding: 2rem var(--section-padding-x);
    margin-top: var(--section-padding-y);
    text-align: center;
}

footer a {
    color: var(--gray-100);
}

footer a:hover {
    color: var(--white);
}

/* ========================================
   Scroll to Top Button
   ======================================== */

.btn-scroll-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 3rem;
    height: 3rem;
    border-radius: var(--border-radius-pill);
    background-color: var(--primary);
    color: var(--white);
    border: none;
    box-shadow: var(--shadow-lg);
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-base);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn-scroll-top.show {
    opacity: 1;
    visibility: visible;
}

.btn-scroll-top:hover {
    background-color: var(--primary-dark);
    transform: translateY(-4px);
    box-shadow: var(--shadow-hover);
}

/* ========================================
   Skip to Content (Accessibility)
   ======================================== */

.skip-to-content {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--primary);
    color: var(--white);
    padding: 8px;
    text-decoration: none;
    z-index: 100;
}

.skip-to-content:focus {
    top: 0;
}

/* ========================================
   Focus Indicators (Accessibility)
   ======================================== */

:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
    border-radius: var(--border-radius-sm);
}

/* ========================================
   Responsive Design
   ======================================== */

/* Mobile phones (portrait) */
@media (max-width: 575.98px) {
    :root {
        --section-padding-y: 2rem;
        --nav-height: 60px;
    }

    body {
        font-size: 0.9375rem;
    }

    h1 { font-size: 1.75rem; }
    h2 { font-size: 1.5rem; }
    h3 { font-size: 1.25rem; }
    h4 { font-size: 1.125rem; }

    .btn-scroll-top {
        width: 2.5rem;
        height: 2.5rem;
        bottom: 1rem;
        right: 1rem;
    }

    .card {
        margin-bottom: 1rem;
    }

    .navbar-brand img {
        height: 40px;
    }
}

/* Tablets (portrait) */
@media (min-width: 576px) and (max-width: 767.98px) {
    :root {
        --section-padding-y: 3rem;
    }

    h1 { font-size: 2rem; }
    h2 { font-size: 1.75rem; }
}

/* Tablets (landscape) and small desktops */
@media (min-width: 768px) and (max-width: 991.98px) {
    :root {
        --section-padding-y: 3.5rem;
    }
}

/* Large desktops */
@media (min-width: 1400px) {
    .container {
        max-width: 1320px;
    }
}

/* Print styles */
@media print {
    .navbar,
    .btn-scroll-top,
    footer {
        display: none;
    }

    body {
        padding-top: 0;
    }

    a {
        text-decoration: underline;
    }

    .card {
        box-shadow: none;
        border: 1px solid var(--gray-300);
    }
}

/* ========================================
   Utility Classes
   ======================================== */

.text-primary { color: var(--primary) !important; }
.bg-primary { background-color: var(--primary) !important; }
.border-primary { border-color: var(--primary) !important; }

.mt-section { margin-top: var(--section-padding-y); }
.mb-section { margin-bottom: var(--section-padding-y); }
.py-section { padding-top: var(--section-padding-y); padding-bottom: var(--section-padding-y); }

/* Smooth fade-in animation */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

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

/* Loading state */
.loading {
    opacity: 0.6;
    pointer-events: none;
}