:root {
    --bg-dark: #FFFFFF;
    --bg-panel: #F9F9F9;
    --bg-component: #FFFFFF;
    --primary: #BC0031;
    --primary-glow: rgba(188, 0, 49, 0.25);
    --accent: #3F6391;
    --accent-glow: rgba(63, 99, 145, 0.35);
    --danger: #BC0031;
    --text-main: #1F1D21;
    --text-muted: #555555;
    --border: #BEC6D1;
    --font-main: "Source Sans 3", "Source Sans Pro", Arial, Helvetica, sans-serif;
    --font-mono: "Courier New", Courier, monospace;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    background-color: var(--bg-dark);
    border-top: 6px solid #BC0031;
    color: var(--text-main);
    font-family: var(--font-main);
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.app-container {
    display: flex;
    flex-direction: column;
    flex: 1;
    min-height: 0;
    padding: 1rem;
    gap: 1rem;
}

/* Header */
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.5rem 1rem;
    background: var(--bg-panel);
    border-radius: 12px;
    border: 1px solid var(--border);
}

h1 {
    font-size: 1.5rem;
    font-weight: 700;
}

.highlight {
    color: var(--primary);
}

.controls {
    display: flex;
    gap: 1rem;
    align-items: center;
}

.btn {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    border-radius: 8px;
    border: none;
    font-family: var(--font-main);
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
}

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

.btn.primary:hover {
    box-shadow: 0 0 15px var(--primary-glow);
}

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

.btn.accent:hover {
    box-shadow: 0 0 15px var(--accent-glow);
}

.btn.secondary {
    background: var(--bg-component);
    color: var(--text-main);
    border: 1px solid var(--border);
}

.btn.secondary:hover {
    background: var(--border);
}

.btn.small {
    padding: 0.25rem 0.75rem;
    font-size: 0.875rem;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    box-shadow: none;
}

/* Main Layout */
.cpu-layout {
    display: grid;
    grid-template-columns: minmax(190px, 300px) minmax(0, 1fr) minmax(190px, 300px);
    gap: 1rem;
    flex: 1;
    min-height: 0;
    /* Fix flex overflow */
}

.panel {
    background: var(--bg-panel);
    border-radius: 12px;
    border: 1px solid var(--border);
    padding: 1rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    overflow: hidden;
}

.panel-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

h2 {
    font-size: 1.1rem;
    color: var(--text-muted);
    font-weight: 600;
}

/* Memory Grid */
.memory-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 0.5rem;
    overflow-y: auto;
    padding-right: 0.5rem;
}

.memory-cell {
    background: var(--bg-component);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 0.5rem;
    font-family: var(--font-mono);
    font-size: 0.75rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    position: relative;
    transition: all 0.3s ease;
}

.memory-cell.active-read {
    border-color: var(--accent);
    box-shadow: 0 0 10px var(--accent-glow);
}

.memory-cell.active-write {
    border-color: var(--accent);
    background: #DCE4EE;
    box-shadow: 0 0 10px var(--accent-glow);
}

.memory-cell.pc-highlight {
    border-color: var(--primary);
    border-width: 2px;
}

.cell-addr {
    font-size: 0.7rem;
    color: var(--text-muted);
    margin-bottom: 2px;
}

.cell-val {
    font-weight: 600;
}

/* CPU Core */
.cpu-core {
    background: #FFFFFF;
    border-radius: 12px;
    border: 1px solid var(--border);
    padding: 2rem;
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 2rem;
    position: relative;
}

.component-group {
    display: flex;
    justify-content: space-around;
    gap: 2rem;
    z-index: 2;
}

.component {
    background: var(--bg-component);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 1rem;
    min-width: 120px;
    text-align: center;
    box-shadow: none;
    transition: all 0.3s ease;
}

.component.active {
    border-color: var(--primary);
    box-shadow: 0 0 15px var(--primary-glow);
    transform: translateY(-2px);
}

.component .label {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
}

.component .value {
    font-size: 1rem;
    font-weight: 600;
    letter-spacing: 1px;
}

.component.large {
    min-width: 200px;
    background: var(--bg-component);
}

.alu-op {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--accent);
}

.decode-hint {
    font-size: 0.8rem;
    color: var(--accent);
    margin-top: 0.2rem;
}

.control-unit {
    align-self: center;
    width: 200px;
    border-color: var(--primary);
    z-index: 2;
    position: relative;
}

.state-indicator {
    font-weight: 700;
    color: var(--primary);
    margin-top: 0.5rem;
}

/* Buses */
.bus-system {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 1;
}

.bus {
    position: absolute;
    background: #E3E7EC;
    transition: all 0.2s ease;
    border-radius: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.7rem;
    color: rgba(31, 29, 33, 0.35);
    font-weight: 700;
    letter-spacing: 1px;
    overflow: hidden;
}

.bus::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(90deg, transparent, rgba(188, 0, 49, 0.25), transparent);
    transform: translateX(-100%);
    transition: transform 0.5s;
}

.bus.active {
    background: var(--primary);
    box-shadow: 0 0 15px var(--primary-glow);
    color: white;
}

.bus.active::after {
    animation: bus-flow 1s infinite linear;
}

@keyframes bus-flow {
    0% {
        transform: translateX(-100%);
    }

    100% {
        transform: translateX(100%);
    }
}

/* Specific Bus Positioning (Approximate for visual layout) */
.data-bus {
    top: 45%;
    left: 10%;
    width: 80%;
    height: 12px;
}

.address-bus {
    top: 25%;
    left: 10%;
    width: 80%;
    height: 8px;
    background: #E3E7EC;
}

.control-bus {
    bottom: 25%;
    left: 10%;
    width: 80%;
    height: 8px;
    background: #E3E7EC;
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(31, 29, 33, 0.45);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 100;
    backdrop-filter: blur(5px);
    opacity: 1;
    transition: opacity 0.3s ease;
}

.modal.hidden {
    opacity: 0;
    pointer-events: none;
}

.modal-content {
    background: var(--bg-panel);
    border: 1px solid var(--border);
    border-radius: 12px;
    width: 500px;
    max-width: 90%;
    max-height: 80vh;
    display: flex;
    flex-direction: column;
    box-shadow: 0 8px 24px rgba(31, 29, 33, 0.18);
}

.modal-header {
    padding: 1rem;
    border-bottom: 1px solid var(--border);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.btn-close {
    background: none;
    border: none;
    color: var(--text-muted);
    font-size: 1.5rem;
    cursor: pointer;
}

.btn-close:hover {
    color: var(--text-main);
}

.modal-body {
    padding: 1rem;
    overflow-y: auto;
}

.opcode-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

.opcode-table th,
.opcode-table td {
    padding: 0.75rem;
    text-align: left;
    border-bottom: 1px solid var(--border);
}

.opcode-table th {
    color: var(--text-muted);
    font-weight: 600;
}

.opcode-table td:first-child {
    font-family: var(--font-mono);
    color: var(--accent);
}


/* IO Panel */
.io-panel {
    gap: 2rem;
}

.io-block h2 {
    margin-bottom: 0.5rem;
}

.input-group {
    display: flex;
    gap: 0.5rem;
}

input[type="number"] {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    color: var(--text-main);
    padding: 0.5rem;
    border-radius: 6px;
    width: 100%;
    font-family: var(--font-mono);
}

.output-display {
    background: #F9F9F9;
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 1rem;
    height: 150px;
    overflow-y: auto;
    color: var(--accent);
    font-size: 0.9rem;
}

.log-list {
    font-size: 0.8rem;
    color: var(--text-muted);
    overflow-y: auto;
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.log-entry {
    border-bottom: 1px solid #E3E7EC;
    padding-bottom: 2px;
}

.font-mono {
    font-family: var(--font-mono);
}

/* Responsive */
/* keep 16-bit values inside their boxes on 4:3 projectors */
.component-group { gap: 1rem; }
.component { padding: 0.75rem; }
.cpu-core { padding: 1.5rem 1rem; }
.io-block.log-block { flex: 1; min-height: 0; display: flex; flex-direction: column; gap: 0.5rem; }

/* phones and narrow windows: stack the three columns and let the page scroll */
@media (max-width: 980px) {
    body { height: auto; min-height: 100vh; overflow: auto; }
    .app-container { padding: 0.5rem; }
    .component-group { flex-wrap: wrap; }
    .cpu-core { min-width: 0; }
    .cpu-layout {
        grid-template-columns: 1fr;
        grid-template-rows: auto auto auto;
    }
    .memory-panel { height: 60vh; }
    .cpu-core { min-height: 520px; }
    header { flex-wrap: wrap; gap: 0.5rem; }
    .controls { flex-wrap: wrap; }
}

/* course style */
input[type=range] { accent-color: #BC0031; }

/* legend under the memory grid */
.legend { display: flex; gap: 1rem; font-size: 0.85rem; color: var(--text-muted); flex-wrap: wrap; }
.legend-item { display: inline-flex; align-items: center; gap: 0.35rem; }
.dot { display: inline-block; width: 14px; height: 14px; border-radius: 4px; background: var(--bg-component); border: 2px solid var(--border); }
.dot.pc-dot { border-color: var(--primary); }
.dot.access-dot { border-color: var(--accent); box-shadow: 0 0 6px var(--accent-glow); }
.dot.write-dot { border-color: var(--accent); background: #DCE4EE; }

/* memory cells: opcode | operand split, and what the bits mean */
.cell-no { color: var(--text-muted); font-family: var(--font-main); font-size: 0.7rem; margin-left: 4px; }
.cell-meaning { font-family: var(--font-main); font-size: 0.8rem; min-height: 1.1em; margin-top: 1px; }
.cell-meaning.is-code { color: var(--accent); font-weight: 700; }
.cell-meaning.is-data { color: var(--text-muted); }