.concurrency-lab {
    margin: 2rem 0;
    padding: 1.5rem;
    border: var(--border-subtle);
    border-radius: var(--radius-lg);
    background:
        radial-gradient(circle at top left, var(--accent-soft), transparent 40%),
        linear-gradient(180deg, var(--surface) 0%, var(--surface-muted) 100%);
    box-shadow: var(--shadow-sm);
}

.concurrency-lab__eyebrow {
    display: inline-block;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-secondary);
    background: var(--surface);
    border: var(--border-subtle);
    padding: 0.2rem 0.6rem;
    border-radius: var(--radius-pill);
    margin-bottom: 0.75rem;
}

.concurrency-lab__title {
    font-family: var(--font-serif);
    font-size: clamp(1.25rem, 2vw, 1.55rem);
    line-height: 1.2;
    margin: 0 0 0.5rem;
    color: var(--text-primary);
}

.concurrency-lab__intro {
    color: var(--text-secondary);
    margin: 0 0 1.25rem;
}

.concurrency-lab__mode-switch {
    display: flex;
    gap: 0.6rem;
    margin-bottom: 1.4rem;
    flex-wrap: wrap;
}

.concurrency-lab__mode-button {
    appearance: none;
    font: inherit;
    font-size: 0.85rem;
    font-weight: var(--font-weight-semibold);
    padding: 0.55rem 1.1rem;
    border-radius: var(--radius-pill);
    border: var(--border-subtle);
    background: var(--surface);
    color: var(--text-secondary);
    cursor: pointer;
    transition: transform 120ms ease, border-color 120ms ease, background-color 120ms ease, color 120ms ease;
}

.concurrency-lab__mode-button:hover {
    transform: translateY(-1px);
    border-color: var(--accent);
}

.concurrency-lab__mode-button:focus-visible {
    outline: 3px solid var(--focus-ring);
    outline-offset: 2px;
}

.concurrency-lab__mode-button.is-active {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--surface);
}

.concurrency-lab__section-label {
    margin: 0 0 0.5rem;
    color: var(--text-secondary);
    font-size: 0.72rem;
    font-weight: var(--font-weight-bold);
    letter-spacing: 0.08em;
    text-transform: uppercase;
}

.concurrency-lab__loop {
    margin-bottom: 1.3rem;
}

.concurrency-lab__loop-track,
.concurrency-lab__lane-track {
    position: relative;
    height: 26px;
    border-radius: var(--radius-sm);
    background: var(--surface);
    border: var(--border-subtle);
    overflow: hidden;
}

.concurrency-lab__loop-segment {
    position: absolute;
    top: 3px;
    bottom: 3px;
    left: 0;
    width: 0;
    border-radius: 4px;
    background: var(--text-primary);
    color: var(--surface);
    font-family: var(--font-mono);
    font-size: 0.62rem;
    display: flex;
    align-items: center;
    justify-content: center;
    white-space: nowrap;
    overflow: hidden;
    opacity: 0.92;
}

.concurrency-lab__lanes {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.concurrency-lab__lane {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.concurrency-lab__lane-label {
    flex: 0 0 auto;
    width: 68px;
    font-family: var(--font-mono);
    font-size: 0.72rem;
    color: var(--text-secondary);
}

.concurrency-lab__lane-track {
    flex: 1 1 auto;
}

.concurrency-lab__lane-wait,
.concurrency-lab__lane-busy {
    position: absolute;
    top: 3px;
    bottom: 3px;
    left: 0;
    width: 0;
    border-radius: 4px;
}

.concurrency-lab__lane-wait {
    background: transparent;
    border: 1px dashed var(--text-secondary);
}

.concurrency-lab__lane-busy {
    background: var(--accent);
    transition: width linear;
}

.concurrency-lab__lane-busy.is-done {
    background: var(--text-primary);
}

.concurrency-lab__log {
    margin: 1.2rem 0 0;
    max-height: 9.5rem;
    overflow-y: auto;
    border: var(--border-subtle);
    border-radius: var(--radius-sm);
    background: var(--surface);
    padding: 0.6rem 0.8rem;
    font-family: var(--font-mono);
    font-size: 0.76rem;
    line-height: 1.55;
    color: var(--text-secondary);
}

.concurrency-lab__log-line {
    white-space: pre-wrap;
}

.concurrency-lab__summary {
    margin-top: 1rem;
    padding: 0.85rem 1rem;
    border: var(--border-subtle);
    border-radius: var(--radius-sm);
    background: var(--surface-muted);
    color: var(--text-primary);
    font-size: 0.92rem;
    line-height: 1.55;
    opacity: 0;
    transform: translateY(4px);
    transition: opacity 250ms ease, transform 250ms ease;
}

.concurrency-lab__summary.is-visible {
    opacity: 1;
    transform: translateY(0);
}

.concurrency-lab__controls {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-top: 1.4rem;
    flex-wrap: wrap;
}

.concurrency-lab__button {
    appearance: none;
    font: inherit;
    font-size: 0.85rem;
    font-weight: var(--font-weight-semibold);
    padding: 0.55rem 1.15rem;
    border-radius: var(--radius-pill);
    border: var(--border-subtle);
    background: var(--accent);
    border-color: var(--accent);
    color: var(--surface);
    cursor: pointer;
    transition: transform 120ms ease, background-color 120ms ease, border-color 120ms ease, opacity 120ms ease;
}

.concurrency-lab__button:hover:not(:disabled) {
    transform: translateY(-1px);
    background: var(--accent-hover);
    border-color: var(--accent-hover);
}

.concurrency-lab__button:focus-visible {
    outline: 3px solid var(--focus-ring);
    outline-offset: 2px;
}

.concurrency-lab__button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}

@media (max-width: 600px) {
    .concurrency-lab__lane-label {
        width: 48px;
        font-size: 0.62rem;
    }
}