/* Basis-Design: ruhig, lesbar, barrierearm – bewusst ohne Framework */

:root {
    --color-bg: #f7f4ef;
    --color-surface: #ffffff;
    --color-text: #1f2a24;
    --color-muted: #4d5a53;
    --color-border: #d5ddd7;
    --color-primary: #1f6b4a;
    --color-primary-hover: #17553a;
    --color-focus: #0b57d0;
    --color-success-bg: #e7f6ec;
    --color-success-border: #2f7d4a;
    --color-error-bg: #f8ecec;
    --color-error-border: #9b3b3b;
    --font-sans: "Roboto Condensed", "Segoe UI", "Helvetica Neue", Arial, sans-serif;
    --font-math: "Roboto Mono", "Consolas", "Courier New", monospace;
    --radius: 0.5rem;
    --space: 1rem;
    --max-width: 48rem;
    --nav-width: 18rem;
    --topbar-height: 4.25rem;
}

*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    font-size: 112.5%;
    line-height: 1.5;
}

body {
    margin: 0;
    min-height: 100vh;
    font-family: var(--font-sans);
    color: var(--color-text);
    background:
        radial-gradient(circle at top left, #e8f2eb 0%, transparent 40%),
        linear-gradient(180deg, #fbfaf7 0%, var(--color-bg) 100%);
}

body.nav-open {
    overflow: hidden;
}

.skip-link {
    position: absolute;
    left: -9999px;
    top: 0;
    background: var(--color-surface);
    color: var(--color-text);
    padding: 0.5rem 1rem;
    z-index: 200;
}

.skip-link:focus {
    left: 0.5rem;
    top: 0.5rem;
}

/* ===== Topbar & Navigation ===== */

.site-chrome {
    position: sticky;
    top: 0;
    z-index: 50;
    background: #fbfaf7;
    border-bottom: 1px solid var(--color-border);
}

.topbar {
    /* Kein backdrop-filter / transform – und Nav liegt bewusst außerhalb von .site-chrome. */
    background: transparent;
    border-bottom: 0;
}

.topbar-inner {
    width: min(100% - 2rem, var(--max-width));
    margin-inline: auto;
    min-height: 3.25rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    padding: 0.65rem 0 0.35rem;
}

.brand-link {
    text-decoration: none;
    color: inherit;
    display: block;
    min-width: 0;
}

.brand {
    margin: 0;
    font-size: 1.15rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    line-height: 1.3;
}

.tagline {
    margin: 0;
    color: var(--color-muted);
    font-size: 0.85rem;
}

.menu-toggle,
.menu-close {
    font: inherit;
    font-weight: 600;
    border: 1px solid var(--color-border);
    border-radius: 0.375rem;
    background: #fff;
    color: var(--color-text);
    cursor: pointer;
    padding: 0.45rem 0.7rem;
}

.menu-toggle {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
}

.menu-toggle-bars {
    width: 1.1rem;
    height: 0.85rem;
    display: inline-block;
    background:
        linear-gradient(var(--color-text), var(--color-text)) 0 0 / 100% 2px no-repeat,
        linear-gradient(var(--color-text), var(--color-text)) 0 50% / 100% 2px no-repeat,
        linear-gradient(var(--color-text), var(--color-text)) 0 100% / 100% 2px no-repeat;
}

.nav-backdrop {
    position: fixed;
    inset: 0;
    background: rgba(20, 30, 24, 0.45);
    z-index: 90;
}

.nav-backdrop[hidden] {
    display: none !important;
}

.site-nav {
    display: flex;
    align-items: center;
}

.site-nav-header {
    display: none;
}

.nav-list {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    align-items: center;
    gap: 0.25rem;
}

.nav-item {
    position: relative;
}

.nav-link,
.nav-dropdown-toggle {
    font: inherit;
    font-weight: 600;
    color: var(--color-text);
    background: transparent;
    border: 0;
    border-radius: 0.375rem;
    padding: 0.45rem 0.7rem;
    cursor: pointer;
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    gap: 0.35rem;
}

.nav-link:hover,
.nav-dropdown-toggle:hover,
.nav-link.is-current,
.has-dropdown.is-current-section > .nav-dropdown-toggle {
    background: #e8f0eb;
}

.nav-caret {
    width: 0.45rem;
    height: 0.45rem;
    border-right: 2px solid currentColor;
    border-bottom: 2px solid currentColor;
    transform: rotate(45deg) translateY(-1px);
}

.nav-dropdown {
    list-style: none;
    margin: 0;
    padding: 0.4rem;
    min-width: 15rem;
    position: absolute;
    top: calc(100% + 0.35rem);
    left: 0;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    box-shadow: 0 8px 24px rgba(31, 42, 36, 0.12);
    display: none;
    z-index: 70;
}

.has-dropdown.is-open > .nav-dropdown {
    display: block;
}

.nav-sublink {
    display: block;
    padding: 0.55rem 0.7rem;
    border-radius: 0.3rem;
    text-decoration: none;
    color: var(--color-text);
}

.nav-sublink:hover,
.nav-sublink.is-current {
    background: #e8f0eb;
}

.nav-sublink.is-disabled {
    color: var(--color-muted);
    cursor: default;
}

.menu-toggle:focus-visible,
.menu-close:focus-visible,
.nav-link:focus-visible,
.nav-dropdown-toggle:focus-visible,
.nav-sublink:focus-visible,
select:focus,
input[type="text"]:focus,
button:focus-visible,
.topic-card:focus-visible {
    outline: 3px solid var(--color-focus);
    outline-offset: 2px;
}

/* ===== Layout ===== */

.site-main,
.site-footer {
    width: min(100% - 2rem, var(--max-width));
    margin-inline: auto;
}

.site-main {
    padding: 1.5rem 0 2rem;
}

.intro h1 {
    margin: 0 0 0.5rem;
    font-size: 1.5rem;
}

.intro p {
    margin: 0 0 1.5rem;
    color: var(--color-muted);
}

.area-overview h2 {
    margin: 0 0 1rem;
    font-size: 1.2rem;
}

.area-list,
.topic-links {
    list-style: none;
    margin: 0;
    padding: 0;
}

.area-group + .area-group {
    margin-top: 1.5rem;
}

.area-group h3 {
    margin: 0 0 0.75rem;
    font-size: 1.05rem;
}

.topic-links {
    display: grid;
    gap: 0.75rem;
}

.topic-card {
    display: block;
    padding: 1rem;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    text-decoration: none;
    color: inherit;
}

.topic-card:hover {
    border-color: #b7c7bc;
    background: #fbfcfb;
}

.topic-card-title {
    display: block;
    font-weight: 700;
    margin-bottom: 0.25rem;
}

.topic-card-text {
    display: block;
    color: var(--color-muted);
    font-size: 0.95rem;
}

.practice {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.25rem;
    box-shadow: 0 1px 0 rgba(31, 42, 36, 0.04);
}

.controls {
    margin-bottom: 1.25rem;
}

.field {
    display: flex;
    flex-direction: column;
    gap: 0.35rem;
}

.field label {
    font-weight: 600;
}

select,
input[type="text"] {
    font: inherit;
    color: inherit;
    padding: 0.6rem 0.75rem;
    border: 1px solid var(--color-border);
    border-radius: 0.375rem;
    background: #fff;
}

input[type="text"]#answer {
    font-family: var(--font-math);
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.02em;
}

.question-label {
    margin: 0;
    color: var(--color-muted);
}

.question-display {
    margin: 0.35rem 0 1.25rem;
}

.question {
    margin: 0;
    font-family: var(--font-math);
    font-size: 1.75rem;
    font-weight: 700;
    letter-spacing: 0.02em;
    font-variant-numeric: tabular-nums;
}

.column-sum {
    display: inline-block;
    font-variant-numeric: tabular-nums;
    font-family: var(--font-math);
    font-size: 1.35rem;
    font-weight: 700;
    line-height: 1.35;
    padding: 0.75rem 1rem;
    background: #f4f8f5;
    border: 1px solid var(--color-border);
    border-radius: 0.4rem;
}

.column-row {
    display: grid;
    grid-template-columns: 1.25rem auto;
    column-gap: 0.5rem;
    justify-content: end;
}

.column-op {
    text-align: center;
}

.column-num {
    text-align: right;
    white-space: pre;
}

.column-line {
    border-top: 2px solid var(--color-text);
    margin: 0.35rem 0;
}

.answer-field {
    margin-top: 0.25rem;
}

.scratchpad-field {
    margin: 1rem 0 1.25rem;
}

.scratchpad-field textarea {
    font: inherit;
    font-family: var(--font-math);
    color: inherit;
    width: 100%;
    min-height: 10rem;
    padding: 0.75rem;
    border: 1px solid var(--color-border);
    border-radius: 0.375rem;
    background: #fbfcfb;
    resize: vertical;
    line-height: 1.45;
}

.scratchpad-field textarea:focus {
    outline: 3px solid var(--color-focus);
    outline-offset: 2px;
}

.hint {
    margin: 0;
    font-size: 0.9rem;
    color: var(--color-muted);
}

.actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 1.25rem;
}

.button {
    font: inherit;
    font-weight: 600;
    border: 2px solid transparent;
    border-radius: 0.375rem;
    padding: 0.65rem 1.1rem;
    cursor: pointer;
}

.button:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.button-primary {
    background: var(--color-primary);
    color: #fff;
}

.button-primary:hover:not(:disabled) {
    background: var(--color-primary-hover);
}

.button-secondary {
    background: #fff;
    color: var(--color-text);
    border-color: var(--color-border);
}

.button-secondary:hover:not(:disabled) {
    background: #f3f6f4;
}

.status {
    margin-bottom: 1rem;
    color: var(--color-muted);
    font-size: 0.95rem;
}

.feedback {
    margin-top: 1.25rem;
    padding: 1rem;
    border-radius: var(--radius);
    border: 2px solid var(--color-border);
    white-space: pre-wrap;
}

.feedback.is-correct {
    background: var(--color-success-bg);
    border-color: var(--color-success-border);
}

.feedback.is-incorrect {
    background: var(--color-error-bg);
    border-color: var(--color-error-border);
}

.feedback-title {
    margin: 0 0 0.5rem;
    font-weight: 700;
}

.feedback-body {
    margin: 0;
    font-family: var(--font-math);
    font-size: 0.95rem;
}

.site-footer {
    padding: 2rem 0;
    color: var(--color-muted);
    font-size: 0.95rem;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* ===== Tablet / Handy: Side-Drawer ===== */

@media (max-width: 896px) {
    .brand {
        font-size: 1rem;
    }

    .menu-toggle {
        display: inline-flex;
        position: relative;
        z-index: 110;
        flex-shrink: 0;
    }

    .site-nav {
        position: fixed;
        top: 0;
        left: 0;
        width: min(100vw - 3rem, var(--nav-width));
        height: 100vh;
        height: 100dvh;
        background: var(--color-surface);
        border-right: 1px solid var(--color-border);
        transform: translateX(-105%);
        transition: transform 0.2s ease, visibility 0.2s ease;
        z-index: 100;
        display: block;
        overflow-y: auto;
        -webkit-overflow-scrolling: touch;
        padding: 1rem;
        visibility: hidden;
        pointer-events: none;
    }

    body.nav-open .site-nav {
        transform: translateX(0);
        visibility: visible;
        pointer-events: auto;
    }

    .site-nav-header {
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: 0.75rem;
        margin-bottom: 1rem;
    }

    .site-nav-title {
        margin: 0;
        font-weight: 700;
    }

    .nav-list {
        flex-direction: column;
        align-items: stretch;
        gap: 0.25rem;
    }

    .nav-link,
    .nav-dropdown-toggle {
        width: 100%;
        justify-content: space-between;
    }

    .nav-dropdown {
        position: static;
        display: none;
        box-shadow: none;
        border: 0;
        border-left: 2px solid var(--color-border);
        border-radius: 0;
        margin: 0.15rem 0 0.35rem 0.5rem;
        padding: 0.15rem 0 0.15rem 0.4rem;
        min-width: 0;
    }

    .has-dropdown.is-open > .nav-dropdown {
        display: block;
    }
}

@media (min-width: 897px) {
    .menu-toggle {
        display: none;
    }

    .nav-backdrop {
        display: none !important;
    }

    .site-chrome {
        border-bottom: 0;
    }

    /* Desktop: eigene Menüzeile unter der Markenzeile (nicht in sticky eingeschlossen) */
    .site-nav {
        position: relative;
        z-index: 40;
        box-sizing: border-box;
        width: 100%;
        margin: 0;
        display: flex;
        align-items: center;
        justify-content: center;
        padding: 0.2rem 0 0.7rem;
        background: #fbfaf7;
        border-bottom: 1px solid var(--color-border);
        pointer-events: auto;
    }

    .site-nav .nav-list {
        width: min(100% - 2rem, var(--max-width));
        margin: 0;
        pointer-events: auto;
        flex-wrap: wrap;
    }

    .site-nav-header {
        display: none;
    }
}

@media (max-width: 40rem) {
    html {
        font-size: 100%;
    }

    .question {
        font-size: 1.5rem;
    }

    .column-sum {
        font-size: 1.2rem;
        width: 100%;
    }

    .actions {
        flex-direction: column;
    }

    .button {
        width: 100%;
    }

    .topic-links {
        grid-template-columns: 1fr;
    }
}

@media (min-width: 40.01rem) {
    .topic-links {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}