/* ── Reiter (Informationen + Übungsreiter) ── */
        .tabbar {
            display: flex;
            gap: 0.5rem;
            margin: 0.4rem 0 1rem;
        }

        .tab {
            flex: 1 1 0;
            min-width: 0;
            min-height: 52px;
            padding: 0.6rem 0.9rem;
            border-radius: var(--radius);
            border: 1px solid var(--border-color);
            background: var(--panel-bg);
            color: var(--text-color);
            font: inherit;
            font-size: 1.02rem;
            font-weight: 700;
            line-height: 1.2;
            cursor: pointer;
            transition: var(--transition-fast);
            box-shadow: var(--shadow-sm);
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            gap: 0.15rem;
            text-align: center;
        }

        .tab:hover {
            border-color: var(--clr-accent);
        }

        .tab.active {
            background: var(--clr-accent);
            color: var(--clr-on-accent);
            border-color: var(--clr-accent);
        }

        .tab .tprog {
            font-size: 0.75rem;
            font-weight: 600;
            color: var(--clr-muted);
        }

        .tab.active .tprog {
            color: inherit;
        }

        .tabpanel {
            display: none;
        }

        .tabpanel.active {
            display: block;
        }

        /* ── Stufen-Navigation je Reiter (sticky) ── */
        .levelnav {
            position: sticky;
            top: 0;
            z-index: 20;
            background: var(--clr-bg);
            padding: 0.45rem 0;
            border-bottom: 1px solid var(--border-color);
            margin-bottom: 1rem;
        }

        .levelnav ul {
            display: flex;
            flex-wrap: wrap;
            gap: 0.4rem;
            list-style: none;
        }

        .levelnav a {
            display: inline-flex;
            align-items: center;
            gap: 0.4rem;
            min-height: 38px;
            padding: 0.25rem 0.75rem 0.25rem 0.3rem;
            border-radius: 999px;
            border: 1px solid var(--border-color);
            background: var(--panel-bg);
            color: var(--text-color);
            text-decoration: none;
            font-size: 0.85rem;
        }

        .levelnav a:hover {
            border-color: var(--clr-accent);
        }

        .levelnav .lnum {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            width: 1.7rem;
            height: 1.7rem;
            border-radius: 999px;
            background: var(--box-bg);
            border: 1px solid var(--border-color);
            font-weight: 700;
        }

        .levelnav a.done {
            border-color: var(--success);
            color: var(--success-text);
        }

        .levelnav a.done .lnum {
            background: var(--success);
            border-color: var(--success);
            color: var(--clr-on-accent);
        }

        .levelnav a .count {
            color: var(--clr-muted);
        }

        /* ── Stufen ── */
        section.level {
            background: var(--clr-surface);
            border: 1px solid var(--border-color);
            border-radius: var(--radius-lg);
            padding: 1.1rem 1.3rem 1.3rem;
            margin: 1.2rem 0;
            box-shadow: var(--shadow-sm);
            scroll-margin-top: 4.5rem;
        }

        section.level h2 {
            font-size: 1.15rem;
            margin: 0.1rem 0 0.3rem;
        }

        .levelmeta {
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
            align-items: baseline;
        }

        .chip {
            display: inline-block;
            padding: 0.12rem 0.6rem;
            border-radius: 999px;
            background: var(--box-bg);
            border: 1px solid var(--border-color);
            color: var(--clr-accent2-text);
            font-size: 0.78rem;
            font-weight: 600;
        }

        p.didaktik {
            margin: 0.6rem 0 0.8rem;
            padding: 0.55rem 0.8rem;
            background: rgba(251, 191, 36, 0.06);
            border-left: 4px solid var(--warning);
            border-radius: 0 8px 8px 0;
            color: var(--text-color);
            font-size: 0.92rem;
            line-height: 1.55;
        }

        p.didaktik b:first-child {
            display: block;
            font-size: 0.8rem;
            text-transform: uppercase;
            letter-spacing: 0.5px;
            color: var(--warning-text);
        }

        details.example {
            background: var(--box-bg);
            border: 1px solid var(--border-color);
            border-radius: var(--radius);
            padding: 0.7rem 1rem;
            margin: 0.8rem 0;
            line-height: 1.55;
        }

        details.example summary {
            cursor: pointer;
            font-weight: 600;
            color: var(--clr-accent-text);
            min-height: 28px;
        }

        details.example p {
            margin: 0.4rem 0;
        }

        /* ── Merksätze, Beispiele, Stolperfallen (Informationen und Stufen) ── */
        .merke,
        .beispiel,
        .stolper {
            margin: 0.9rem 0;
            padding: 0.65rem 0.9rem;
            line-height: 1.55;
        }

        .merke {
            border: 2px solid var(--clr-accent);
            border-radius: 10px;
            background: color-mix(in srgb, var(--clr-accent) 8%, transparent);
        }

        .beispiel {
            border-left: 4px solid var(--clr-accent2);
            border-radius: 0 10px 10px 0;
            background: var(--box-bg);
        }

        .stolper {
            border-left: 4px solid var(--danger);
            border-radius: 0 10px 10px 0;
            background: rgba(248, 113, 113, 0.06);
        }

        .merke::before,
        .beispiel::before,
        .stolper::before {
            display: block;
            font-size: 0.75rem;
            font-weight: 800;
            letter-spacing: 0.06em;
            text-transform: uppercase;
            margin-bottom: 0.2rem;
        }

        .merke::before {
            content: "Merke";
            color: var(--clr-accent-text);
        }

        .beispiel::before {
            content: "Beispiel";
            color: var(--clr-accent2-text);
        }

        .stolper::before {
            content: "Stolperfalle";
            color: var(--danger-text);
        }

        .merke p,
        .beispiel p,
        .stolper p {
            margin: 0.3rem 0;
        }

        /* ── Reiter Informationen ── */
        section.info {
            background: var(--clr-surface);
            border: 1px solid var(--border-color);
            border-radius: var(--radius-lg);
            padding: 1.1rem 1.4rem 1.2rem;
            margin: 1.2rem 0;
            box-shadow: var(--shadow-sm);
            scroll-margin-top: 1rem;
            line-height: 1.6;
        }

        section.info h2 {
            font-size: 1.2rem;
            color: var(--clr-accent-text);
            margin-bottom: 0.5rem;
        }

        section.info h3 {
            font-size: 1.02rem;
            margin: 1.1rem 0 0.3rem;
        }

        section.info p {
            margin: 0.5rem 0;
        }

        section.info ul,
        section.info ol {
            margin: 0.4rem 0 0.6rem;
            padding-left: 1.4rem;
        }

        section.info li {
            margin: 0.2rem 0;
        }

        .info-cols {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(min(100%, 21rem), 1fr));
            gap: 0 1.4rem;
        }

        .toc {
            display: flex;
            flex-wrap: wrap;
            gap: 0.4rem;
            list-style: none;
            padding: 0 !important;
        }

        .toc a {
            display: inline-block;
            padding: 0.35rem 0.75rem;
            border-radius: 999px;
            border: 1px solid var(--border-color);
            background: var(--box-bg);
            color: var(--text-color);
            text-decoration: none;
            font-size: 0.88rem;
        }

        .toc a:hover {
            border-color: var(--clr-accent);
        }

        ol.path {
            list-style: none;
            padding: 0 !important;
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(min(100%, 15rem), 1fr));
            gap: 0.5rem;
            counter-reset: step;
        }

        ol.path li {
            margin: 0 !important;
        }

        ol.path a {
            display: flex;
            gap: 0.6rem;
            align-items: center;
            height: 100%;
            padding: 0.5rem 0.7rem;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: var(--box-bg);
            color: var(--text-color);
            text-decoration: none;
            line-height: 1.3;
        }

        ol.path a:hover {
            border-color: var(--clr-accent);
        }

        ol.path a::before {
            counter-increment: step;
            content: counter(step);
            flex: none;
            display: inline-flex;
            align-items: center;
            justify-content: center;
            width: 1.8rem;
            height: 1.8rem;
            border-radius: 999px;
            background: var(--clr-accent);
            color: var(--clr-on-accent);
            font-weight: 700;
        }

        ol.path small {
            display: block;
            color: var(--clr-muted);
        }

        a.goto {
            display: inline-flex;
            align-items: center;
            min-height: 40px;
            margin-top: 0.4rem;
            padding: 0.35rem 0.85rem;
            border-radius: 9px;
            border: 1px solid var(--clr-accent);
            color: var(--clr-accent-text);
            text-decoration: none;
            font-weight: 600;
            font-size: 0.92rem;
        }

        a.goto:hover {
            background: var(--box-bg);
        }

        .rules-table {
            border-collapse: collapse;
            margin: 0.6rem 0;
        }

        .rules-table th,
        .rules-table td {
            border: 1px solid var(--border-color);
            padding: 0.3rem 0.7rem;
            text-align: center;
        }

        .rules-table th {
            background: var(--box-bg);
            color: var(--clr-accent2-text);
        }

        .rules-table td.mono,
        .mono {
            font-family: 'Courier New', monospace;
            font-weight: 600;
        }

        details.teacher {
            background: var(--clr-surface);
            border: 1px solid var(--border-color);
            border-radius: var(--radius-lg);
            padding: 0.9rem 1.3rem;
            margin: 1.2rem 0;
            line-height: 1.6;
        }

        details.teacher summary {
            cursor: pointer;
            font-weight: 700;
            color: var(--clr-accent-text);
            min-height: 28px;
        }

        details.teacher h3 {
            margin: 1rem 0 0.3rem;
            font-size: 1rem;
        }

        details.teacher p {
            margin: 0.5rem 0;
        }

        details.teacher ul {
            padding-left: 1.3rem;
        }

        details.teacher li {
            margin: 0.3rem 0;
        }

        /* ── Bit-Baukasten (zum Ausprobieren im Reiter Informationen) ── */
        .bitlab {
            margin: 0.9rem 0;
            padding: 0.8rem 0.9rem;
            border: 1px dashed var(--clr-accent2);
            border-radius: 12px;
            background: var(--box-bg);
        }

        .bitlab .bl-title {
            font-weight: 700;
            color: var(--clr-accent2-text);
            margin-bottom: 0.4rem;
        }

        .bitrow {
            display: grid;
            grid-template-columns: repeat(8, minmax(0, 1fr));
            gap: 0.3rem;
            max-width: 32rem;
        }

        .bitrow.q4 {
            grid-template-columns: repeat(4, minmax(0, 1fr)) 0.5rem repeat(4, minmax(0, 1fr));
        }

        .bitrow .w {
            font-size: 0.72rem;
            text-align: center;
            color: var(--clr-muted);
            line-height: 1.2;
            align-self: end;
        }

        .bitrow .comma {
            text-align: center;
            font-weight: 800;
            font-size: 1.3rem;
            align-self: center;
        }

        .bitbtn {
            min-height: 46px;
            min-width: 0;
            font-family: 'Courier New', monospace;
            font-size: 1.25rem;
            font-weight: 700;
            border-radius: 8px;
            border: 1px solid var(--border-color);
            background: var(--panel-bg);
            color: var(--text-color);
            cursor: pointer;
        }

        .bitbtn[aria-pressed="true"] {
            background: var(--clr-accent);
            border-color: var(--clr-accent);
            color: var(--clr-on-accent);
        }

        .bitlab .bl-actions {
            display: flex;
            flex-wrap: wrap;
            gap: 0.4rem;
            margin-top: 0.6rem;
        }

        .bitlab .bl-out {
            margin-top: 0.6rem;
            font-size: 0.95rem;
        }

        .bitlab .bl-out b {
            font-family: 'Courier New', monospace;
        }

        /* ── Aufgabenkarten ── */
        article.task {
            border: 1px solid var(--border-color);
            border-radius: var(--radius);
            padding: 0.9rem 1.05rem 1.05rem;
            margin: 0.9rem 0;
            background: var(--box-bg);
        }

        article.task.solved {
            border-color: var(--success);
        }

        .task-head {
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            gap: 0.2rem 0.6rem;
            align-items: baseline;
        }

        .task-head .ttitle {
            font-weight: 700;
            color: var(--clr-accent-text);
        }

        .task-head .tstate {
            font-size: 0.82rem;
            color: var(--clr-muted);
        }

        article.task.solved .tstate {
            color: var(--success-text);
            font-weight: 600;
        }

        .prompt {
            margin: 0.5rem 0 0.7rem;
            line-height: 1.6;
        }

        .bits {
            background: rgba(56, 189, 248, 0.12);
            color: var(--clr-accent2-text);
            border-radius: 5px;
            padding: 0.05rem 0.35rem;
            font-family: 'Courier New', monospace;
            font-weight: 600;
            letter-spacing: 0.5px;
            white-space: nowrap;
        }

        .fields {
            display: flex;
            flex-wrap: wrap;
            gap: 0.8rem 1.4rem;
            margin: 0.4rem 0 0.8rem;
        }

        .field {
            min-width: 0;
            max-width: 100%;
        }

        .field.f-radios {
            flex: 1 1 100%;
        }

        .field > label,
        .field .flabel {
            display: block;
            font-size: 0.88rem;
            color: var(--clr-muted);
            margin-bottom: 0.25rem;
        }

        .field input[type=text] {
            display: block;
            margin-top: 0.25rem;
            font-size: 1.05rem;
            min-height: 44px;
            padding: 0.4rem 0.6rem;
            border: 1px solid var(--border-color);
            border-radius: 8px;
            background: var(--panel-bg);
            color: var(--text-color);
            width: 14rem;
            font-family: 'Courier New', monospace;
        }

        .bitcount {
            display: block;
            min-height: 1.1em;
            margin-top: 0.2rem;
            font-size: 0.78rem;
            color: var(--clr-muted);
        }

        .bitcount.full {
            color: var(--success-text);
        }

        .bitcount.over {
            color: var(--danger-text);
        }

        .radios {
            display: flex;
            flex-direction: column;
            gap: 0.4rem;
            max-width: 48rem;
        }

        .radios label {
            display: flex;
            gap: 0.6rem;
            align-items: flex-start;
            min-height: 44px;
            padding: 0.55rem 0.75rem;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: var(--panel-bg);
            color: var(--text-color);
            font-size: 0.95rem;
            line-height: 1.45;
            cursor: pointer;
        }

        .radios label:hover {
            border-color: var(--clr-accent);
        }

        .radios label:has(input:checked) {
            border-color: var(--clr-accent);
            box-shadow: inset 0 0 0 1px var(--clr-accent);
        }

        .radios input[type=radio] {
            flex: none;
            width: 1.15rem;
            height: 1.15rem;
            margin-top: 0.15rem;
            accent-color: var(--clr-accent);
        }

        .btnrow {
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
        }

        .btnrow button,
        .levelfoot button,
        .bitlab .bl-actions button {
            font: inherit;
            cursor: pointer;
            min-height: 44px;
            border-radius: 9px;
            padding: 0.45rem 0.95rem;
            border: 1px solid var(--border-color);
            background: var(--panel-bg);
            color: var(--text-color);
        }

        .btnrow button:hover,
        .levelfoot button:hover,
        .bitlab .bl-actions button:hover {
            border-color: var(--clr-accent);
        }

        .btnrow button.primary {
            background: var(--clr-accent);
            border-color: var(--clr-accent);
            color: var(--clr-on-accent);
            font-weight: 600;
        }

        .btnrow button:disabled {
            opacity: 0.5;
            cursor: default;
        }

        .feedback:empty {
            display: none;
        }

        .feedback {
            margin: 0.7rem 0 0;
            padding: 0.55rem 0.8rem;
            border-radius: 8px;
            font-size: 0.95rem;
            line-height: 1.5;
        }

        .feedback.ok {
            background: rgba(52, 211, 153, 0.08);
            border: 1px solid var(--success);
            color: var(--success-text);
        }

        .feedback.err {
            background: rgba(248, 113, 113, 0.08);
            border: 1px solid var(--danger);
            color: var(--danger-text);
        }

        .feedback ul {
            margin: 0.3rem 0 0;
            padding-left: 1.2rem;
        }

        .tips {
            margin: 0.7rem 0 0;
            padding: 0.55rem 0.8rem;
            background: rgba(251, 191, 36, 0.06);
            border-left: 4px solid var(--warning);
            border-radius: 0 8px 8px 0;
            font-size: 0.93rem;
            line-height: 1.5;
            color: var(--text-color);
        }

        .tips .tlabel {
            font-weight: 700;
            display: block;
            color: var(--warning-text);
            margin-bottom: 0.2rem;
        }

        .tips p {
            margin: 0.3rem 0;
        }

        .solution {
            margin: 0.8rem 0 0;
            padding: 0.7rem 0.9rem;
            background: rgba(52, 211, 153, 0.05);
            border: 1px solid var(--border-color);
            border-left: 4px solid var(--success);
            border-radius: 0 8px 8px 0;
            font-size: 0.94rem;
            line-height: 1.55;
        }

        .solution[hidden] {
            display: none;
        }

        .solution .slabel {
            font-weight: 700;
            color: var(--success-text);
            display: block;
            margin-bottom: 0.3rem;
        }

        .solution p {
            margin: 0.4rem 0;
        }

        .solution ol,
        .solution ul {
            margin: 0.3rem 0;
            padding-left: 1.4rem;
        }

        .solution ol li,
        .solution ul li {
            margin: 0.15rem 0;
        }

        pre.bins {
            display: inline-block;
            max-width: 100%;
            overflow-x: auto;
            vertical-align: top;
            background: var(--panel-bg);
            border: 1px solid var(--border-color);
            border-radius: 6px;
            padding: 0.5rem 0.8rem;
            font-size: 1.02rem;
            line-height: 1.45;
            margin: 0.3rem 0 0.5rem;
            letter-spacing: 1px;
            font-family: 'Courier New', monospace;
            color: var(--text-color);
        }

        .sol-note {
            color: var(--clr-muted);
            font-size: 0.9rem;
        }

        .levelfoot {
            margin-top: 1rem;
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
            justify-content: space-between;
            align-items: center;
        }

        .levelfoot a.goto {
            margin-top: 0;
            min-height: 44px;
        }

        /* ── Tablet und Smartphone ── */
        @media (max-width: 640px) {
            .tabbar {
                gap: 0.35rem;
            }

            .tab {
                padding: 0.45rem 0.25rem;
                font-size: 0.86rem;
                hyphens: auto;
                overflow-wrap: anywhere;
            }

            .levelnav .lname {
                display: none;
            }

            .levelnav a {
                padding-right: 0.6rem;
            }

            section.level,
            section.info {
                padding: 0.9rem 0.85rem 1rem;
            }

            details.teacher {
                padding: 0.8rem 0.85rem;
            }

            article.task {
                padding: 0.8rem 0.75rem 0.9rem;
            }

            .field {
                flex: 1 1 100%;
            }

            .field input[type=text] {
                width: 100%;
            }

            .btnrow button {
                flex: 1 1 auto;
            }

            .levelfoot > * {
                flex: 1 1 100%;
                justify-content: center;
            }

            .rules-table {
                font-size: 0.82rem;
            }

            .rules-table th,
            .rules-table td {
                padding: 0.25rem 0.3rem;
            }

            pre.bins {
                font-size: 0.92rem;
                letter-spacing: 0.5px;
                padding: 0.45rem 0.55rem;
            }

            .bitbtn {
                font-size: 1.05rem;
            }
        }