/* ============================================================
   FLASHCARD DESIGN TOKENS
   ============================================================ */
:root {
    --card-width: clamp(300px, 82vw, 560px);
    --card-aspect: 1.9 / 1;

    --card-radius: 1.6rem;
    --card-font: clamp(1.05rem, 1.4vw, 1.35rem);

    --card-border: var(--surface-border);
    --card-shadow: var(--shadow-elevated);
    --card-shadow-hover: var(--shadow-elevated);
    --card-glow: 0 0 0 1px var(--surface-border);

    --ghost-step: 0.42rem;

    --tone-strong: var(--accent-primary);
    --tone-strong-soft: color-mix(in srgb, var(--accent-primary), var(--surface-muted) 35%);
    --tone-muted: color-mix(in srgb, var(--text-primary), var(--surface-muted) 55%);
    --tone-border: var(--surface-border);
    --tone-success: var(--accent-success);
    --tone-danger: var(--accent-danger);
}

/* ============================================================
   CORE LAYOUT
   ============================================================ */

.card-wrapper {
    perspective: clamp(800px, 120vw, 1200px);
}

.card-stack {
    position: relative;
    width: var(--card-width);
    aspect-ratio: var(--card-aspect);
}

/* ============================================================
   CARD
   ============================================================ */

.card {
    position: absolute;
    inset: 0;

    transform-style: preserve-3d;
    -webkit-transform-style: preserve-3d;
    will-change: transform;
    transition: transform 0.5s ease, box-shadow 0.5s ease;

    background: transparent;
    border-radius: var(--card-radius);
    border: 1px solid var(--card-border);
    box-shadow: var(--card-shadow), var(--card-glow);
    cursor: pointer;
    overflow: hidden;
}

.card:hover {
    box-shadow: var(--card-shadow-hover), var(--card-glow);
}

.card.no-flip-transition,
.card.no-flip-transition .side {
    transition: none !important;
}

.card:not(.flip):hover {
    transform: translateY(-4px);
}

.card.flip:hover {
    transform: translateY(-2px);
}

.flip {
    transform: none;
}

.card::before,
.card::after {
    content: none;
}

/* ============================================================
   CARD SIDES
   ============================================================ */

.side {
    position: absolute;
    inset: 0;

    display: flex;
    align-items: center;
    justify-content: center;

    padding: clamp(1.25rem, 2.6vw, 2rem);
    font-size: var(--card-font);
    line-height: 1.5;
    text-align: center;

    border-radius: inherit;
    transform-style: preserve-3d;
    backface-visibility: hidden !important;
    -webkit-backface-visibility: hidden !important;
    letter-spacing: 0.01em;
    z-index: 1;
    transition: transform 0.45s ease, opacity 0.45s ease;
}

.front {
    background: var(--surface-base);
    color: var(--text-primary);
    transform: rotateY(0deg);
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    opacity: 1;
}

.back {
    background: var(--surface-elevated);
    color: var(--accent-primary);
    transform: rotateY(180deg);
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    transform-style: preserve-3d;
    opacity: 0;
}

/* Flip visibility swap (fallback if 3D is flattened) */
.card.flip .front {
    transform: rotateY(180deg);
    opacity: 0;
}

.card.flip .back {
    transform: rotateY(0deg);
    opacity: 1;
}

/* Force correct backface handling across browsers */
#card {
    transform-style: preserve-3d;
    -webkit-transform-style: preserve-3d;
}

/* ============================================================
   FLASHCARD DESCRIPTION (STABLE)
   ============================================================ */

.flashcard-center-stack {
    display: flex;
    flex-direction: column;
    align-items: center;
    overflow-anchor: none;
}

.flashcard-center-stack.match-only .card-stack,
.flashcard-center-stack.match-only .flashExplanation-wrap {
    display: none;
}

.flashcard-center-stack.match-only .flashcards-description {
    margin-bottom: 0.9rem;
}

.flashcard-center-stack.match-only .study-buttons {
    margin-top: 0.2rem;
}

body.match-mode #progress {
    display: none;
}

/* DEBUG 3D: force preserve-3d on ancestors */
.flashcard-center-stack,
.card-stack,
.card-wrapper {
    transform-style: preserve-3d !important;
    -webkit-transform-style: preserve-3d !important;
}

.flashcards-description {
    max-width: var(--card-width);
    width: 100%;

    min-height: 6rem;
    margin-bottom: 1.4rem;
    padding: 1.1rem 1.4rem;

    font-size: clamp(0.95rem, 1vw, 1.1rem);
    line-height: 1.6;
    text-align: center;
    color: var(--text-secondary);

    background:
        linear-gradient(140deg,
            color-mix(in srgb, var(--text-primary), transparent 88%),
            transparent 55%),
        var(--surface-base);
    border-radius: 0.9rem;
    border: 1px solid var(--surface-border);
    box-shadow: var(--shadow-soft);

    opacity: 0;
    transform: translateY(-0.75rem);
    visibility: hidden;
    pointer-events: none;

    transition:
        opacity 0.45s ease,
        transform 0.45s ease,
        visibility 0s linear 0.45s;
}

.flashcards-description.show-desc {
    opacity: 1;
    transform: translateY(0);
    visibility: visible;
    pointer-events: auto;
}

.flashcards-description.hide-desc,
.flashcards-description.hidden-desc {
    opacity: 0;
    transform: translateY(-0.75rem);
    visibility: hidden;
    pointer-events: none;
}

/* ============================================================
   EXPLANATION AREA
   ============================================================ */

.flashExplanation-wrap {
    margin-top: 2.5rem;
    max-width: min(64ch, 92%);
    width: 100%;
    height: auto;
    text-align: center;

    font-size: clamp(0.9rem, 1vw, 1.05rem);
    line-height: 1.55;
    color: var(--text-secondary);

    transition: opacity 0.35s ease;
}

.flashExplanation-wrap.hidden-meta .flash-meta-title,
.flashExplanation-wrap.hidden-meta .flash-meta-box {
    opacity: 0;
    pointer-events: none;
}

.flashExplanation-wrap.hidden-meta #flashExplanation,
.flashExplanation-wrap.hidden-meta .flash-formula {
    visibility: hidden;
}

#flashExplanation {
    padding: 0.9rem 1.15rem;
    background:
        linear-gradient(145deg,
            color-mix(in srgb, var(--text-primary), transparent 90%),
            transparent 70%),
        var(--surface-base);
    border: 1px solid var(--surface-border);
    border-radius: 0.9rem;
    box-shadow: var(--shadow-soft);
    height: 100%;
    overflow: auto;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.35s ease;
}

.flash-meta-row {
    display: grid;
    grid-template-columns: 1fr;
    gap: 12px;
    align-items: stretch;
}

.flash-meta-row.no-formula {
    grid-template-columns: 1fr;
}

.flash-meta-box {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.flash-meta-title {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-secondary);
    padding: 0 0.2rem;
}

.formula-box.hidden {
    display: none;
}

.flash-formula {
    padding: 0.9rem 1rem;
    background:
        linear-gradient(145deg,
            color-mix(in srgb, var(--text-primary), transparent 90%),
            transparent 70%),
        var(--surface-base);
    border: 1px solid var(--surface-border);
    border-radius: 0.9rem;
    box-shadow: var(--shadow-soft);
    min-height: 72px;
    overflow: auto;
}

.flash-formula.collapsed {
    max-height: 0;
    padding-top: 0;
    padding-bottom: 0;
    border-width: 0;
    overflow: hidden;
}

.formula-toggle {
    border: 1px solid var(--surface-border);
    background: var(--surface-base);
    color: var(--text-secondary);
    border-radius: 999px;
    padding: 4px 10px;
    font-size: 0.75rem;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.formula-toggle:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-soft);
}

@media (max-width: 900px) {
    .flash-meta-row {
        grid-template-columns: 1fr;
    }
}

/* ============================================================
   GHOST STACK
   ============================================================ */

.card.ghost {
    position: absolute;
    inset: 0;
    pointer-events: none;

    background: var(--surface-base);
    border: 1px solid var(--surface-border);
    border-radius: var(--card-radius);

    box-shadow: var(--shadow-soft);
    backdrop-filter: blur(10px);

    filter: saturate(0.9) brightness(0.9);
    opacity: 0;
    transition: opacity 0.25s ease;
}

.card.ghost.visible {
    opacity: 1;
}

.ghost-1 {
    transform: translateY(calc(var(--ghost-step) * 1)) rotate(-0.2deg) scale(0.985);
}

.ghost-2 {
    transform: translateY(calc(var(--ghost-step) * 2)) rotate(0.25deg) scale(0.97);
}

.ghost-3 {
    transform: translateY(calc(var(--ghost-step) * 3)) rotate(-0.35deg) scale(0.955);
}

.ghost-4 {
    transform: translateY(calc(var(--ghost-step) * 4)) rotate(0.4deg) scale(0.94);
}

.card.ghost::after {
    content: "";
    position: absolute;
    inset: 0;
    border-radius: inherit;
    box-shadow: inset 0 1px 0 color-mix(in srgb, var(--text-primary), transparent 88%);
}

/* ============================================================
   STACK ADVANCE
   ============================================================ */

.card.ghost.advance {
    animation: stackAdvance 0.35s ease;
}

@keyframes stackAdvance {
    from {
        transform: translateY(calc(var(--ghost-step) * 2)) scale(0.97);
    }

    to {
        transform: translateY(calc(var(--ghost-step) * 1)) scale(0.985);
    }
}

/* ============================================================
   SWIPE NAVIGATION
   ============================================================ */

.card.swipe-left {
    animation: swipeLeft 0.35s ease forwards;
}

.card.swipe-right {
    animation: swipeRight 0.35s ease forwards;
}

@keyframes swipeLeft {
    to {
        transform: translateX(-120%) rotate(-6deg) scale(0.96);
        opacity: 0;
    }
}

@keyframes swipeRight {
    to {
        transform: translateX(120%) rotate(6deg) scale(0.96);
        opacity: 0;
    }
}

/* ============================================================
   ENTRANCE ANIMATIONS
   ============================================================ */

.fadeIn {
    opacity: 0;
    animation: fadeIn 0.6s ease-out forwards;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(0.5rem);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.slideInLeft {
    opacity: 0;
    animation: slideInLeft 0.6s ease-out forwards;
}

@keyframes slideInLeft {
    from {
        opacity: 0;
        transform: translateX(-1.25rem);
    }

    to {
        opacity: 1;
        transform: translateX(0);
    }
}

/* ============================================================
   MATH BLOCK
   ============================================================ */

.math-block {
    margin: 0.5rem 0;
    text-align: center;
}

/* ============================================================
   STUDY MODE BUTTONS
   ============================================================ */

.study-buttons {
    margin-top: 1.25rem;
    display: none;
    text-align: center;
}

.study-mode-block {
    display: none;
}

.tf-hint {
    font-size: 0.9rem;
    opacity: 0.65;
    margin-bottom: 0.75rem;
}

.study-hint {
    font-size: 0.9rem;
    opacity: 0.78;
    margin-bottom: 0.75rem;
}

.study-hint-strong {
    font-size: 0.98rem;
    color: var(--text-primary);
}

.study-hint-strong strong {
    color: var(--tone-strong);
    font-weight: 600;
}


.study-btn {
    padding: 0.8rem 1.45rem;
    font-size: clamp(0.95rem, 1vw, 1.1rem);
    border-radius: 999px;
    border: none;
    cursor: pointer;
    color: var(--text-on-accent);
    letter-spacing: 0.01em;
    box-shadow: var(--shadow-soft);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.study-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-elevated);
}

.study-reset {
    background: color-mix(in srgb, var(--surface-muted), var(--accent-primary) 18%);
    color: var(--text-primary);
}

.match-actions {
    display: flex;
    justify-content: center;
    margin-bottom: 0.75rem;
}

.study-reveal {
    background: var(--tone-strong);
}

.study-hint-btn {
    background: color-mix(in srgb, var(--accent-primary), var(--surface-muted) 55%);
    color: var(--text-primary);
    padding-inline: 1.1rem;
}

.study-hint-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-elevated);
}

.study-answer-buttons {
    margin-top: 1.1rem;
    display: none;
    width: 100%;
    max-width: 26rem;
    margin-inline: auto;

    display: flex;
    justify-content: space-between;
    gap: 1.25rem;
}

.study-wrong {
    background: linear-gradient(135deg, var(--tone-danger), var(--tone-muted));
    color: var(--text-on-danger);
}

.study-correct {
    background: linear-gradient(135deg, var(--tone-success), var(--tone-strong));
    color: var(--text-on-success);
}

.study-input-row {
    display: flex;
    gap: 10px;
    align-items: center;
    justify-content: center;
    max-width: 520px;
    margin: 0 auto;
    flex-wrap: wrap;
}

.study-write-cloze {
    margin: 0.5rem auto 0.85rem;
    max-width: 640px;
    text-align: center;
    font-size: clamp(0.95rem, 1.1vw, 1.1rem);
    color: var(--text-secondary);
}

.study-blank-token {
    display: inline-block;
    padding: 0 0.35rem;
    border-bottom: 2px solid color-mix(in srgb, var(--accent-primary), transparent 45%);
    color: var(--text-primary);
    font-weight: 600;
}

.study-write-blanks {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: center;
    max-width: 720px;
    margin: 0 auto 0.75rem;
}

.study-write-blank {
    min-width: 120px;
    padding: 0.65rem 0.8rem;
    border-radius: 10px;
    border: 1px solid var(--surface-border);
    background: var(--surface-base);
    color: var(--text-primary);
    outline: none;
    scroll-margin-top: calc(var(--toolbar-height) + 12px);
}

.study-write-blank::placeholder {
    color: color-mix(in srgb, var(--text-primary), transparent 55%);
}

.study-input {
    flex: 1;
    min-width: 0;
    padding: 0.75rem 0.9rem;
    border-radius: 12px;
    border: 1px solid var(--surface-border);
    background: var(--surface-base);
    color: var(--text-primary);
    outline: none;
    scroll-margin-top: calc(var(--toolbar-height) + 12px);
}

.study-input::placeholder {
    color: color-mix(in srgb, var(--text-primary), transparent 55%);
}

.study-feedback {
    margin-top: 1rem;
    font-size: 0.95rem;
    min-height: 1.3rem;
    color: var(--text-secondary);
}

.study-feedback[data-state="correct"] {
    color: var(--tone-success);
}

.study-feedback[data-state="wrong"] {
    color: var(--tone-danger);
}

.study-feedback[data-state="hint"] {
    color: var(--tone-strong);
}

.match-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
    width: 100%;
    max-width: var(--card-width);
    margin: 0 auto;
}

.match-col-header {
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-secondary);
    padding: 0 0.25rem;
    text-align: left;
}

.match-spacer {
    min-height: 44px;
}

/* ===============================
   RESPONSIVE TUNING
   =============================== */

@media (max-width: 700px) {
    .study-input-row {
        gap: 8px;
    }

    .match-grid {
        gap: 10px;
    }

    .match-item {
        padding: 8px 10px;
        font-size: 0.95rem;
    }
}

@media (max-width: 520px) {
    .study-input-row {
        flex-direction: column;
        align-items: stretch;
    }

    .study-input,
    .study-btn {
        width: 100%;
    }

    .match-col-header {
        text-align: center;
    }
}

@media (min-width: 1200px) {
    :root {
        --card-width: clamp(340px, 60vw, 640px);
        --card-font: clamp(1.1rem, 1.2vw, 1.5rem);
    }
}

.match-item {
    padding: 10px 12px;
    border-radius: 12px;
    background: var(--surface-hover);
    cursor: pointer;
    transition: all .15s ease;
    border: 1px solid var(--surface-border);
    color: var(--text-primary);
}

.match-item.active {
    background: color-mix(in srgb, var(--accent-primary), transparent 75%);
    box-shadow: inset 0 0 0 2px color-mix(in srgb, var(--accent-primary), transparent 45%);
}

.match-item.selectable {
    border-color: color-mix(in srgb, var(--tone-success), var(--surface-border) 45%);
    box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--tone-success), transparent 55%);
}

.match-item.locked {
    opacity: 0.45;
    cursor: pointer;
    background: var(--surface-muted);
}

.match-item.locked:hover {
    opacity: 0.65;
}

/* =========================================
   MANUAL CARD INPUTS (THEME-AWARE)
========================================= */

.manual-card-row {
    padding: 15px;
    margin-bottom: 15px;
    background: var(--surface-elevated);
    border-radius: 10px;
    border: 1px solid var(--surface-border);
    box-shadow: var(--shadow-soft);
}

.manual-card-row label {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.manual-input {
    width: 100%;
    padding: 8px;
    padding-right: 0;
    margin-top: 4px;
    margin-bottom: 8px;
    border: 1px solid var(--surface-border);
    border-radius: 8px;
    background: var(--surface-base);
    color: var(--text-primary);
    outline: none;
    transition:
        border-color 0.2s ease,
        box-shadow 0.2s ease,
        background 0.2s ease;
}

.manual-input::placeholder {
    color: var(--text-secondary);
}

.manual-input:focus {
    border-color: color-mix(in srgb, var(--accent-primary), var(--surface-border) 45%);
    background: var(--surface-elevated);
    box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent-primary), transparent 78%);
}

/* =========================================
   AI GENERATION OVERLAY (THEME-AWARE)
========================================= */

:root {
    --ai-bg-start: color-mix(in srgb, var(--accent-primary), transparent 55%);
    --ai-bg-mid: color-mix(in srgb, var(--accent-primary), transparent 75%);
    --ai-bg-end: color-mix(in srgb, var(--text-primary), transparent 85%);
    --ai-glow-opacity: 0.35;
    --ai-radius: clamp(18px, 3vw, 26px);
    --ai-padding: clamp(24px, 5vw, 48px);
}

.ai-gen-root {
    position: relative;
    width: 100%;
    min-height: min(70vh, 520px);
    border-radius: var(--ai-radius);
    overflow: hidden;
    background: var(--surface-base);
}

.ai-gen-bg {
    position: absolute;
    inset: -40%;
    background: linear-gradient(
        120deg,
        var(--ai-bg-start),
        var(--ai-bg-mid),
        var(--ai-bg-end)
    );
    filter: blur(clamp(80px, 18vw, 140px));
    opacity: var(--ai-glow-opacity);
    animation: aiGradientSpin 14s linear infinite;
}

@keyframes aiGradientSpin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

.ai-gen-content {
    position: relative;
    z-index: 1;
    padding: var(--ai-padding);
    text-align: center;
    color: var(--text-primary);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: clamp(12px, 3vw, 22px);
    width: min(720px, 92vw);
    min-height: clamp(420px, 70vh, 560px);
}

.ai-gen-title {
    font-size: clamp(1.4rem, 4vw, 2rem);
    font-weight: 600;
}

.ai-gen-meta {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 0.6em;
    font-size: clamp(0.85rem, 2.5vw, 0.95rem);
    color: var(--text-secondary);
}

.ai-gen-meta li {
    padding: 0.35rem 0.75rem;
    border-radius: 999px;
    background: color-mix(in srgb, var(--surface-muted), transparent 35%);
    border: 1px solid color-mix(in srgb, var(--surface-border), transparent 35%);
}

.ai-gen-phase {
    font-size: clamp(0.95rem, 2.6vw, 1.1rem);
    font-weight: 600;
    color: var(--text-primary);
    opacity: 0.9;
    margin-top: -4px;
    min-height: 1.6em;
    max-width: min(520px, 92%);
    overflow: hidden;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
}

.ai-gen-checklist {
    list-style: none;
    margin: 0;
    padding: 0;
    width: min(460px, 92%);
    display: grid;
    gap: 10px;
    text-align: left;
    color: var(--text-secondary);
}

.ai-gen-checklist li {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 8px 12px;
    border-radius: 12px;
    border: 1px solid color-mix(in srgb, var(--surface-border), transparent 35%);
    background: color-mix(in srgb, var(--surface-muted), transparent 40%);
    font-size: clamp(0.9rem, 2.7vw, 1rem);
    opacity: 0.7;
    transition: opacity 0.25s ease, border-color 0.25s ease, background 0.25s ease;
}

.ai-gen-checklist li::before {
    content: "○";
    font-size: 0.95rem;
    color: var(--text-secondary);
}

.ai-gen-checklist li.active {
    opacity: 1;
    color: var(--text-primary);
    border-color: color-mix(in srgb, var(--accent-primary), transparent 45%);
}

.ai-gen-checklist li.done {
    opacity: 1;
    color: var(--text-primary);
    background: color-mix(in srgb, var(--tone-success), transparent 78%);
    border-color: color-mix(in srgb, var(--tone-success), transparent 55%);
}

.ai-gen-checklist li.done::before {
    content: "✓";
    color: var(--tone-success);
    font-weight: 700;
}

.ai-gen-step {
    font-size: clamp(1rem, 3.5vw, 1.25rem);
    min-height: 2.8em;
    max-height: 2.8em;
    opacity: 0;
    transform: translateY(6px);
    transition: opacity 0.35s ease, transform 0.35s ease;
    overflow: hidden;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
}

.ai-gen-step.show {
    opacity: 1;
    transform: translateY(0);
}

.ai-gen-bar {
    width: min(280px, 70%);
    height: clamp(5px, 1.2vw, 7px);
    border-radius: 999px;
    background: color-mix(in srgb, var(--surface-border), transparent 40%);
    overflow: hidden;
}

.ai-gen-bar-fill {
    width: 0%;
    height: 100%;
    background: linear-gradient(
        90deg,
        var(--accent-primary),
        color-mix(in srgb, var(--accent-primary), transparent 35%),
        color-mix(in srgb, var(--text-primary), transparent 55%)
    );
    transition: width 0.28s ease;
}

.ai-gen-bar-fill.indeterminate {
    width: 40%;
    animation: aiBarSlide 1.4s ease-in-out infinite;
}

.ai-gen-root.fullscreen {
    position: fixed;
    inset: 0;
    width: 100vw;
    height: 100dvh;
    min-height: 100dvh;
    border-radius: 0;
    z-index: 3000;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow-y: auto;
    padding:
        calc(env(safe-area-inset-top, 0px) + 10px)
        12px
        calc(env(safe-area-inset-bottom, 0px) + 10px);
    overscroll-behavior: contain;
}

@media (max-width: 760px) {
    .ai-gen-root.fullscreen {
        align-items: flex-start;
    }

    .ai-gen-content {
        width: min(100%, 680px);
        min-height: 0;
        margin: 0 auto;
        padding: clamp(18px, 4vw, 24px);
        gap: 12px;
    }

    .ai-gen-title {
        font-size: clamp(1.2rem, 5vw, 1.45rem);
    }

    .ai-gen-meta {
        gap: 0.45rem;
    }

    .ai-gen-checklist {
        width: 100%;
        max-height: min(34dvh, 260px);
        overflow-y: auto;
        padding-right: 4px;
    }

    .ai-gen-step {
        min-height: 2.4em;
        max-height: 3.6em;
        -webkit-line-clamp: 3;
    }

    .ai-gen-bar {
        width: min(320px, 92%);
    }
}

@keyframes aiBarSlide {
    0% { transform: translateX(-120%); }
    50% { transform: translateX(60%); }
    100% { transform: translateX(180%); }
}

/* ============================================================
   TRUE/FALSE SWIPE (TINDER-STYLE)
   ============================================================ */

.card.tf-dragging {
    transition: none !important;
    will-change: transform;
}

.card.tf-swipe-right {
    transform: translateX(120%) rotate(12deg);
    transition: transform 0.2s ease;
}

.card.tf-swipe-left {
    transform: translateX(-120%) rotate(-12deg);
    transition: transform 0.2s ease;
}

/* ============================================================
   TRUE/FALSE FEEDBACK
   ============================================================ */

.card.tf-correct {
    animation: tfPulseCorrect 0.45s ease;
    box-shadow: 0 0 0 2px var(--tone-success), var(--shadow-elevated);
}

.card.tf-wrong {
    animation: tfPulseWrong 0.45s ease;
    box-shadow: 0 0 0 2px var(--tone-danger), var(--shadow-elevated);
}

/* True/False flash overlay */
.card.tf-correct::after,
.card.tf-wrong::after {
    content: "";
    position: absolute;
    inset: 0;
    border-radius: inherit;
    pointer-events: none;
    opacity: 0;
    z-index: 2;
    animation: tfFlash 0.75s ease;
}

.card.tf-correct::after {
    background: color-mix(in srgb, var(--tone-success), transparent 78%);
}

.card.tf-wrong::after {
    background: color-mix(in srgb, var(--tone-danger), transparent 78%);
}

@keyframes tfFlash {
    0% {
        opacity: 0;
    }

    30% {
        opacity: 0.75;
    }

    100% {
        opacity: 0;
    }
}

@keyframes tfPulseCorrect {
    0% {
        transform: scale(1);
    }

    40% {
        transform: scale(1.02);
    }

    100% {
        transform: scale(1);
    }
}

@keyframes tfPulseWrong {
    0% {
        transform: translateX(0);
    }

    20% {
        transform: translateX(-6px);
    }

    40% {
        transform: translateX(6px);
    }

    60% {
        transform: translateX(-4px);
    }

    80% {
        transform: translateX(4px);
    }

    100% {
        transform: translateX(0);
    }
}

/* =========================================
   EMPTY FLASHCARD PROMPT
========================================= */

.empty-flashcard-panel {
    padding: clamp(28px, 6vw, 40px);
    max-width: 620px;
    margin: 70px auto;
    text-align: center;

    background: var(--surface-elevated);
    border-radius: 18px;
    border: 1px solid var(--surface-border);

    box-shadow: var(--shadow-elevated);
    animation: fadeIn 0.3s ease;
}

.empty-flashcard-icon {
    font-size: 60px;
    margin-bottom: 14px;
    opacity: 0.85;
}

.empty-flashcard-title {
    font-size: 1.75rem;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.empty-flashcard-text {
    font-size: 1.05rem;
    color: var(--text-secondary);
    margin-bottom: 28px;
}

/* Buttons */

.empty-flashcard-btn {
    width: 100%;
    padding: 14px;
    font-size: 1.05rem;
    border-radius: 14px;
    border: 1px solid var(--surface-border);
    cursor: pointer;
    transition: var(--transition-medium);
    margin-bottom: 12px;
}

.empty-flashcard-btn.primary {
    background: var(--accent-primary);
    color: var(--text-on-accent);
    border-color: transparent;
}

.empty-flashcard-btn.secondary {
    background: var(--accent-primary);
    color: var(--text-on-accent);
    border-color: transparent;
}

.empty-flashcard-btn.muted {
    background: var(--accent-primary);
    color: var(--text-on-accent);
    border-color: transparent;
}

/* Hover lift already exists, but just in case */
.hover-lift:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-soft);
}