/* --- 1. Root Variables & Global Styles --- */
:root {
    --primary-font: 'Merriweather', serif; /* Better for reading long paragraphs */
    --heading-font: 'Lato', sans-serif;
    --background-color: #fcfdfe;
    --container-bg: #ffffff;
    --text-color: #343a40;
    --heading-color: #005f73;
    --accent-color: #0a9396;
    --accent-light: #94d2bd;
    --subtle-accent: #e9f5f5;
    --border-color: #dee2e6;
    --shadow-color-light: rgba(0, 95, 115, 0.08);
    --shadow-color-dark: rgba(0, 95, 115, 0.15);
}

* {
    box-sizing: border-box;
    scroll-behavior: smooth; /* Smooth scrolling for TOC links */
}

body {
    font-family: var(--primary-font);
    line-height: 1.8;
    margin: 0;
    padding: 1rem;
    background-color: var(--background-color);
    color: var(--text-color);
}

/* --- 2. Main Layout & Container --- */
.container {
    max-width: 900px;
    margin: 3rem auto;
    background: var(--container-bg);
    padding: 2rem 3rem;
    border-radius: 12px;
    box-shadow: 0 6px 30px var(--shadow-color-light);
    border: 1px solid var(--border-color);
    position: relative;
}

header h1 {
    text-align: center;
    font-family: var(--heading-font);
    font-size: 3rem;
    color: var(--heading-color);
    margin-bottom: 2.5rem;
    border-bottom: 3px solid var(--accent-light);
    padding-bottom: 1rem;
    font-weight: 700;
}

section {
    margin-top: 3.5rem;
}

footer {
    text-align: center;
    margin-top: 4rem;
    color: #6c757d;
    font-size: 0.9rem;
    border-top: 1px solid var(--border-color);
    padding-top: 1.5rem;
}

/* --- 3. Table of Contents (TOC) --- */
.toc {
    position: sticky;
    top: 20px;
    width: 200px;
    float: left;
    margin-left: -240px; /* Position it outside the main content area */
    background: #f8f9fa;
    padding: 1rem;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}
.toc h3 {
    margin-top: 0;
    font-size: 1.2rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}
.toc ul {
    list-style: none;
    padding: 0;
    margin: 0;
}
.toc li a {
    text-decoration: none;
    color: var(--heading-color);
    font-family: var(--heading-font);
    font-size: 0.95rem;
    display: block;
    padding: 0.5rem;
    border-radius: 5px;
    transition: all 0.2s ease-in-out;
}
.toc li a:hover {
    background-color: var(--subtle-accent);
    color: var(--accent-color);
    transform: translateX(5px);
}

/* --- 4. Typography --- */
h2, h3, h4, h5 {
    font-family: var(--heading-font);
    color: var(--heading-color);
    font-weight: 700;
}

h2 {
    font-size: 2.2rem;
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 0.75rem;
    margin-bottom: 2rem;
}

h3 { font-size: 1.7rem; color: #0077b6; }
h4 { font-size: 1.4rem; color: #0096c7; }
p, li { font-size: 1.1rem; margin-bottom: 1.25rem; }
a { color: var(--accent-color); text-decoration: none; }
a:hover { text-decoration: underline; }

/* --- 5. Table Styling --- */
.table-container { overflow-x: auto; }
table {
    width: 100%;
    border-collapse: collapse;
    margin: 2rem 0;
    font-size: 0.95rem;
    box-shadow: 0 4px 15px var(--shadow-color-light);
    border-radius: 8px;
    overflow: hidden; /* Important for border-radius */
}
th, td {
    border: 1px solid var(--border-color);
    padding: 0.85rem;
    text-align: center;
    transition: background-color 0.2s ease;
}
thead {
    background: linear-gradient(to right, var(--heading-color), var(--accent-color));
    color: white;
}
caption {
    caption-side: bottom;
    padding-top: 1rem;
    font-size: 0.9rem;
    color: #6c757d;
    font-style: italic;
}
tbody tr:nth-child(even) { background-color: #f8f9fa; }
tbody tr:hover { background-color: var(--subtle-accent); }

/* --- 6. Special Content Blocks (Theorem & Proof) --- */
.theorem {
    border-left: 5px solid var(--accent-color);
    padding: 1.5rem 2rem;
    margin: 2rem 0 1rem 0;
    background-color: var(--subtle-accent);
    border-radius: 0 8px 8px 0;
}
.theorem h4 { margin-top: 0; }
.proof summary {
    font-family: var(--heading-font);
    font-size: 1.2rem;
    font-weight: bold;
    color: var(--heading-color);
    cursor: pointer;
    padding: 0.75rem 1.5rem;
    background-color: #f1f3f5;
    border-radius: 8px;
    transition: background-color 0.2s ease;
    list-style: none; /* Hide default marker */
}
.proof summary::before {
    content: '+';
    margin-right: 0.75rem;
    font-weight: bold;
    display: inline-block;
    transition: transform 0.2s ease-in-out;
}
.proof[open] > summary::before {
    transform: rotate(45deg);
}
.proof summary:hover { background-color: #e9ecef; }
.proof > div {
    padding: 1.5rem;
    margin-top: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: 8px;
}

/* --- 7. Diagrams and SVG --- */
.svg-container {
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 2rem 0;
    padding: 1rem;
    background: #fdfdfd;
    border: 1px solid var(--border-color);
    border-radius: 8px;
}

/* --- 8. Interactive Graph Plotter --- */
#graph-container {
    margin-top: 2rem;
    padding: 1.5rem;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background-color: #fdfdfd;
    box-shadow: 0 4px 15px var(--shadow-color-light);
}
.controls {
    display: flex; flex-wrap: wrap; gap: 1rem; align-items: center; margin-bottom: 1.5rem;
}
.controls label {
    font-weight: bold; font-family: var(--heading-font); color: var(--heading-color);
}
.controls select, .controls button {
    padding: 0.6rem 1.2rem;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    font-size: 1rem;
    font-family: var(--heading-font);
    cursor: pointer;
    background-color: var(--container-bg);
    transition: all 0.2s ease-in-out;
}
.controls button:hover, .controls select:hover {
    border-color: var(--accent-color);
    background-color: var(--accent-color);
    color: white;
}
.controls button:active { transform: translateY(2px); }

/* --- 9. Responsive Design --- */
@media (max-width: 1200px) {
    .container {
        max-width: 800px;
    }
    .toc {
        position: static;
        width: 100%;
        float: none;
        margin-left: 0;
        margin-bottom: 2.5rem;
    }
}
@media (max-width: 768px) {
    body { padding: 0.5rem; }
    .container { padding: 1.5rem; margin: 1rem auto; }
    header h1 { font-size: 2.2rem; }
    h2 { font-size: 1.8rem; }
    p, li { font-size: 1rem; }
    .controls { flex-direction: column; align-items: stretch; }
}