/* --- General & Layout --- */
:root {
    --bg-color: #f8f9fa;
    --text-color: #212529;
    --header-bg: #e9ecef;
    --border-color: #dee2e6;
    --accent-color: #007bff;
    --accent-color-light: #cce5ff;
    --highlight-bg: #fff3cd;
    --match-color: #28a745;
    --mismatch-color: #dc3545;
    --arrow-color: #6c757d;
    --trace-path-color: var(--accent-color);
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --box-shadow: 0 2px 4px rgba(0,0,0,0.075);
    --border-radius: 0.3rem;
    --correct-bg: #d4edda;
    --correct-text: #155724;
    --incorrect-bg: #f8d7da;
    --incorrect-text: #721c24;
}

.dark-mode {
    --bg-color: #1e1e1e;
    --text-color: #e0e0e0;
    --header-bg: #2d2d2d;
    --border-color: #444;
    --accent-color: #0d6efd;
    --accent-color-light: #032a5c;
    --highlight-bg: #49411f;
    --match-color: #198754;
    --mismatch-color: #bb2d3b;
    --arrow-color: #888;
    --trace-path-color: var(--accent-color);
    --correct-bg: #198754;
    --correct-text: #fff;
    --incorrect-bg: #bb2d3b;
    --incorrect-text: #fff;
}

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    padding: 1rem;
    transition: background-color 0.3s, color 0.3s;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

main {
    display: grid;
    grid-template-columns: 1fr 2fr;
    grid-template-areas:
        "controls visual"
        "explanation visual"
        "analytics visual";
    gap: 1rem;
    height: calc(100vh - 8rem);
}

@media (max-width: 1200px) {
    main {
        grid-template-columns: 1fr;
        grid-template-areas: "controls" "visual" "explanation" "analytics";
        height: auto;
    }
}

.panel {
    background-color: var(--header-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 1rem;
    box-shadow: var(--box-shadow);
    overflow: auto;
}

h1, h2, h3 { margin-top: 0; }
button, select, input {
    font-family: inherit; font-size: 0.95rem; padding: 0.5rem 0.75rem;
    border-radius: var(--border-radius); border: 1px solid var(--border-color);
    background-color: var(--bg-color); color: var(--text-color);
    cursor: pointer; transition: background-color 0.2s, border-color 0.2s;
}
button:hover:not(:disabled) { background-color: var(--border-color); }
button:disabled { opacity: 0.5; cursor: not-allowed; }
button.primary { background-color: var(--accent-color); color: white; border-color: var(--accent-color); }
button.primary:hover:not(:disabled) { background-color: #0056b3; }

/* --- Controls --- */
header { text-align: center; }
#controls-panel { grid-area: controls; }
.control-group { margin-bottom: 1rem; }
.control-group h3 { margin-bottom: 0.5rem; }
.control-group > div { display: flex; flex-wrap: wrap; gap: 0.5rem; }
.control-group label { display: flex; align-items: center; gap: 0.25rem; }
.control-group input[type="text"] { width: 100%; box-sizing: border-box; }
.control-group input[type="range"] { flex-grow: 1; }
#step-counter { font-weight: bold; }

/* --- Explanation & Analytics --- */
#explanation-panel { grid-area: explanation; }
#explanation-panel .code { background-color: var(--bg-color); padding: 0.5em; border-radius: var(--border-radius); font-family: monospace; white-space: pre-wrap; }
#analytics-panel { grid-area: analytics; }

/* --- Matrix Grid & Visuals --- */
#visual-panel { grid-area: visual; position: relative; overflow: auto; display: flex; flex-direction: column; gap: 1rem; }
#matrix-grid-container { position: relative; width: fit-content; height: fit-content; }
#matrix-grid { border-collapse: collapse; }

#matrix-grid td, #matrix-grid th {
    border: 1px solid var(--border-color);
    width: 50px; height: 50px;
    text-align: center;
    position: relative; /* Crucial for positioning the arrow */
    transition: background-color 0.3s ease;
    padding: 0;
}

#matrix-grid th { background-color: var(--header-bg); font-weight: bold; }

.matrix-cell.current { background-color: var(--highlight-bg); }
.matrix-cell.dependency { background-color: var(--accent-color-light); }
.matrix-cell.traceback-cell { background-color: rgba(0, 123, 255, 0.2); }

/* Validation Styles */
.matrix-cell.correct { background-color: var(--correct-bg); }
.matrix-cell.correct .matrix-cell-content { color: var(--correct-text); font-weight: bold; }
.matrix-cell.incorrect { background-color: var(--incorrect-bg); }
.matrix-cell.incorrect .matrix-cell-content { color: var(--incorrect-text); font-weight: bold; }


/* UPDATED: Center the number and make it larger */
.matrix-cell-content {
    font-size: 1.2rem;
    font-weight: 500;
    position: relative;
    z-index: 2;
}

/* UPDATED: Position the SVG container in the top-left */
.arrow-svg {
    position: absolute;
    top: 2px;
    left: 2px;
    width: 18px; /* Fixed small size */
    height: 18px;
    z-index: 1;
}

.arrow-svg line {
    stroke: var(--arrow-color);
    stroke-width: 1.5;
    marker-end: url(#arrow-head);
    transition: stroke 0.3s, stroke-width 0.3s;
}

.arrow-svg.traceback-arrow line {
    stroke: var(--trace-path-color);
    stroke-width: 2.5;
    marker-end: url(#arrow-head-trace);
}

.arrow-head-fill { fill: var(--arrow-color); transition: fill 0.3s; }
.arrow-head-trace-fill { fill: var(--trace-path-color); transition: fill 0.3s; }

.final-lcs-display { font-size: 1.2rem; font-weight: bold; padding-top: 1rem; }
.final-lcs-display .match { color: var(--match-color); }

/* --- Pseudo-code Panel --- */
#pseudocode-panel { background-color: #272822; color: #f8f8f2; padding: 1rem; border-radius: var(--border-radius); font-family: 'Courier New', Courier, monospace; white-space: pre; overflow-x: auto; margin-top: 1rem; }
.code-line { transition: background-color 0.3s; padding: 0 0.5rem; display: block; }
.code-line.active { background-color: #49483e; border-left: 3px solid var(--accent-color); }