/* MIT PHYSICS ACADEMIC THEME - NATIVE PRINT EDITION
   Design: Minimalist, Content-First, Vector-Perfect
*/

:root {
    /* Academic Palette */
    --bg-canvas: #ffffff;
    --text-primary: #0a0a0a;     /* Near Black */
    --text-body: #222222;        /* High Contrast Grey */
    --text-meta: #555555;
    --link-academic: #003366;    /* Oxford/Academic Blue */
    --border-subtle: #eeeeee;
    --border-strong: #dddddd;

    /* Typography - Screen */
    --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-serif: "Georgia", "Times New Roman", Times, serif;
    
    /* Layout Dimensions */
    --read-width: 760px;
    --nav-height: 80px;
}

/* --- RESET & BASE --- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
    background-color: var(--bg-canvas);
    color: var(--text-body);
    font-family: var(--font-sans);
    font-size: 18px; 
    line-height: 1.75;
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
}

/* --- NAVIGATION --- */
nav {
    position: sticky;
    top: 0;
    background: rgba(255, 255, 255, 0.98);
    border-bottom: 1px solid var(--border-subtle);
    height: var(--nav-height);
    z-index: 1000;
    display: flex;
    align-items: center;
    transition: all 0.3s ease; /* Added for smooth resizing on mobile */
}

.nav-container {
    width: 100%;
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.site-identity {
    font-family: var(--font-sans);
    font-weight: 700;
    font-size: 1rem;
    letter-spacing: -0.02em;
    color: var(--text-primary);
    text-decoration: none;
}

.nav-links { display: flex; gap: 2.5rem; list-style: none; }

.nav-links a {
    text-decoration: none;
    color: var(--text-meta);
    font-size: 0.9rem;
    font-weight: 500;
    transition: color 0.2s ease;
}

.nav-links a:hover, .nav-links a.active { color: var(--link-academic); }

/* --- GLOBAL LAYOUT --- */
.container {
    max-width: var(--read-width);
    margin: 0 auto;
    padding: 4rem 1.5rem 8rem 1.5rem;
}

.fade-in { animation: fadeIn 0.8s cubic-bezier(0.16, 1, 0.3, 1) forwards; opacity: 0; transform: translateY(10px); }
@keyframes fadeIn { to { opacity: 1; transform: translateY(0); } }

/* --- TYPOGRAPHY --- */
h1, h2, h3 {
    font-family: var(--font-serif);
    color: var(--text-primary);
    font-weight: normal;
}

h1 { font-size: 2.8rem; margin-bottom: 1.5rem; letter-spacing: -0.02em; line-height: 1.2; }
h2 { font-size: 1.8rem; margin-top: 4rem; margin-bottom: 1.5rem; border-bottom: 1px solid var(--border-subtle); padding-bottom: 0.5rem; }
h3 { font-size: 1.3rem; margin-top: 2.5rem; margin-bottom: 1rem; font-weight: 600; }

p { margin-bottom: 1.5rem; text-align: justify; }
ul, ol { margin-bottom: 1.5rem; margin-left: 1.5rem; }
li { margin-bottom: 0.5rem; }

/* --- ACADEMIC COMPONENTS --- */
.abstract-box {
    margin: 2.5rem 0;
    padding: 2rem;
    background: #fafafa;
    border-left: 3px solid var(--link-academic);
    font-family: var(--font-serif);
    font-style: italic;
    font-size: 1rem;
    color: var(--text-meta);
}

.math-block {
    margin: 2rem 0;
    overflow-x: auto;
    text-align: center;
    font-family: "Times New Roman", serif;
}

.meta-header {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-subtle);
}

.label-text {
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-meta);
}

.btn-action {
    background: transparent;
    border: 1px solid var(--border-strong);
    padding: 0.5rem 1rem;
    font-size: 0.85rem;
    cursor: pointer;
    border-radius: 3px;
    font-family: var(--font-sans);
    transition: all 0.2s;
}

.btn-action:hover {
    border-color: var(--link-academic);
    color: var(--link-academic);
    background: #f8faff;
}

/* --- NOTES LIBRARY STRUCTURE --- */
.library-layout {
    display: flex;
    gap: 4rem;
    margin-top: 2rem;
}

.library-sidebar {
    width: 250px;
    flex-shrink: 0;
    border-right: 1px solid var(--border-subtle);
    padding-right: 2rem;
}

.sidebar-btn {
    display: block;
    width: 100%;
    text-align: left;
    background: none;
    border: none;
    padding: 0.8rem 0;
    font-size: 0.95rem;
    color: var(--text-meta);
    cursor: pointer;
    font-family: var(--font-sans);
    transition: color 0.2s;
    border-bottom: 1px solid transparent;
}

.sidebar-btn:hover { color: var(--link-academic); }
.sidebar-btn.active { 
    color: var(--text-primary); 
    font-weight: 600; 
    border-left: 3px solid var(--link-academic); 
    padding-left: 10px;
}

.library-content { flex-grow: 1; }
.note-entry { display: none; }
.note-entry.active { display: block; animation: fadeIn 0.5s ease; }

/* --- RESPONSIVE & MOBILE OPTIMIZATION --- */
@media (max-width: 850px) {
    /* 1. LIBRARY LAYOUT FIX */
    .library-layout { flex-direction: column; }
    .library-sidebar { 
        width: 100%; 
        border-right: none; 
        border-bottom: 1px solid var(--border-subtle); 
        padding-bottom: 1.5rem; 
        margin-bottom: 2rem;
    }

    /* 2. NAVIGATION BAR FIX (Mobile/Tablet) */
    nav {
        height: auto; /* Allow height to expand */
        padding: 1rem 0;
    }

    .nav-container {
        flex-direction: column; /* Stack logo and links */
        gap: 1rem;
    }

    .site-identity {
        width: 100%;
        text-align: center;
        padding-bottom: 0.8rem;
        border-bottom: 1px solid var(--border-subtle);
        margin-bottom: 0.5rem;
    }

    .nav-links {
        width: 100%;
        justify-content: center; /* Center the links */
        gap: 1.5rem;
        flex-wrap: wrap; /* Allow wrapping on very small screens */
    }

    .nav-links li {
        margin-bottom: 0;
    }

    .nav-links a {
        font-size: 0.95rem; /* Slightly larger hit area for touch */
        padding: 0.5rem;
    }
}

/* ==========================================================================
   NATIVE BROWSER PRINT ENGINE (CRITICAL)
   This CSS takes over when window.print() is called.
   ========================================================================== */

@media print {
    /* 1. Page Setup */
    @page {
        size: A4 portrait;
        margin: 25mm; /* Standard Academic Margins */
    }

    /* 2. Reset Layout for Paper */
    body {
        background: white;
        color: black;
        font-family: "Times New Roman", Times, serif; /* Force Serif */
        font-size: 11.5pt; /* Standard Journal Size */
        line-height: 1.6;
        width: 100%;
        margin: 0;
        padding: 0;
    }

    /* 3. Hide UI Elements */
    nav, 
    .library-sidebar, 
    .btn-action, 
    footer,
    .label-text { 
        display: none !important; 
    }

    /* 4. Content Isolation Logic 
       We only show the article that has the .print-target class
    */
    body.is-printing > * { display: none; } /* Hide all body children... */
    body.is-printing main { display: block !important; margin: 0 !important; padding: 0 !important; } /* ...except main */
    
    main > * { display: none; } /* Hide all articles... */
    .note-entry.print-target, 
    article.print-target { 
        display: block !important; 
        position: static !important;
        width: 100% !important;
        margin: 0 !important;
        padding: 0 !important;
    }

    /* 5. Typography & Spacing Fixes */
    h1 { font-size: 24pt; text-align: center; margin-bottom: 24pt; color: black; }
    h2 { font-size: 16pt; margin-top: 24pt; border-bottom: 1px solid #000; color: black; page-break-after: avoid; }
    h3 { font-size: 13pt; margin-top: 18pt; color: black; page-break-after: avoid; }
    p { text-align: justify; widows: 3; orphans: 3; }
    a { text-decoration: none; color: black; }

    /* 6. Abstract Specifics */
    .abstract-box {
        border: none;
        background: none;
        padding: 0 40pt;
        font-size: 10.5pt;
        margin-bottom: 30pt;
    }

    /* 7. MATH PROTECTION RULES */
    .math-block, mjx-container {
        page-break-inside: avoid !important;
        margin: 18pt 0 !important;
    }
    
    /* Ensure inline math doesn't overlap lines */
    mjx-container[jax="CHTML"][display="true"] { 
        margin: 1em 0 !important; 
    }
}