/* ===== RESET & BASE ===== */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --green: #58CC02;
    --green-dark: #46a302;
    --green-light: #d7ffb8;
    --red: #FF4B4B;
    --red-dark: #ea2b2b;
    --red-light: #ffdfe0;
    --gold: #FFC800;
    --gold-dark: #e0a800;
    --blue: #1CB0F6;
    --blue-dark: #0995d6;
    --purple: #CE82FF;
    --bg: #131F24;
    --bg-card: #1a2e38;
    --bg-elevated: #223a47;
    --text: #FFFFFF;
    --text-muted: #9CAEB8;
    --text-dark: #1a2e38;
    --radius: 16px;
    --radius-sm: 12px;
    --shadow: 0 4px 0 rgba(0, 0, 0, 0.25);
    --shadow-lg: 0 8px 0 rgba(0, 0, 0, 0.2);
    --font: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
}

body {
    font-family: var(--font);
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    overflow-x: hidden;
}

/* ===== TOP BAR ===== */
#top-bar {
    position: sticky;
    top: 0;
    z-index: 100;
    width: 100%;
    max-width: 600px;
    padding: 16px 20px 12px;
    display: flex;
    align-items: center;
    gap: 16px;
    background: var(--bg);
}

#progress-section {
    flex: 1;
    display: flex;
    align-items: center;
    gap: 10px;
}

#progress-bar-track {
    flex: 1;
    height: 16px;
    background: var(--bg-elevated);
    border-radius: 999px;
    overflow: hidden;
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.3);
}

#progress-bar-fill {
    height: 100%;
    width: 0%;
    background: linear-gradient(90deg, var(--green), #7ad940);
    border-radius: 999px;
    transition: width 0.6s cubic-bezier(0.22, 1, 0.36, 1);
    position: relative;
}

#progress-bar-fill::after {
    content: '';
    position: absolute;
    top: 3px;
    left: 6px;
    right: 6px;
    height: 4px;
    background: rgba(255, 255, 255, 0.3);
    border-radius: 999px;
}

#progress-label {
    font-size: 0.8rem;
    font-weight: 700;
    color: var(--text-muted);
    white-space: nowrap;
}

#stats {
    display: flex;
    gap: 12px;
}

#stats>div {
    display: flex;
    align-items: center;
    gap: 4px;
    font-weight: 800;
    font-size: 0.95rem;
}

.stat-icon {
    font-size: 1.1rem;
}

#hearts-count {
    color: var(--red);
}

#xp-count {
    color: var(--gold);
}

#streak-count {
    color: #FF9600;
}

/* ===== MAIN ===== */
#app {
    width: 100%;
    max-width: 600px;
    padding: 8px 20px 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
    flex: 1;
}

/* ===== PROBLEM CARD ===== */
#problem-card {
    width: 100%;
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius);
    padding: 28px 24px 24px;
    text-align: center;
    margin-bottom: 28px;
    box-shadow: var(--shadow);
    position: relative;
    overflow: hidden;
}

#problem-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--blue), var(--purple), var(--green));
}

#problem-label {
    font-size: 0.85rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1.5px;
    color: var(--text-muted);
    margin-bottom: 16px;
}

#problem-integral {
    font-size: 1.8rem;
    line-height: 1.6;
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* ===== STEP SECTION ===== */
#step-section {
    width: 100%;
    margin-bottom: 20px;
}

#step-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    margin-bottom: 8px;
}

#step-prompt {
    font-size: 1.2rem;
    font-weight: 800;
    text-align: center;
    line-height: 1.4;
    color: var(--text);
    margin-bottom: 0;
}

#hint-btn {
    flex-shrink: 0;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border: 2px solid rgba(255, 200, 0, 0.4);
    background: rgba(255, 200, 0, 0.1);
    font-size: 1.2rem;
    cursor: pointer;
    transition: all var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    -webkit-tap-highlight-color: transparent;
}

#hint-btn:hover {
    background: rgba(255, 200, 0, 0.25);
    border-color: var(--gold);
    transform: scale(1.1);
    box-shadow: 0 0 12px rgba(255, 200, 0, 0.3);
}

#hint-btn:active {
    transform: scale(0.95);
}

#hint-btn.active {
    background: rgba(255, 200, 0, 0.25);
    border-color: var(--gold);
    box-shadow: 0 0 12px rgba(255, 200, 0, 0.3);
}

#hint-bubble {
    width: 100%;
    background: rgba(255, 200, 0, 0.08);
    border: 1.5px solid rgba(255, 200, 0, 0.25);
    border-radius: var(--radius-sm);
    padding: 16px 18px;
    margin-bottom: 16px;
    animation: hintSlideIn 0.3s cubic-bezier(0.22, 1, 0.36, 1);
    position: relative;
}

#hint-bubble::before {
    content: '💡';
    position: absolute;
    top: -10px;
    left: 16px;
    font-size: 0.9rem;
    background: var(--bg);
    padding: 0 6px;
}

#hint-content {
    font-size: 0.9rem;
    line-height: 1.6;
    color: var(--text);
    opacity: 0.92;
}

#hint-content strong {
    color: var(--gold);
    font-weight: 700;
}

@keyframes hintSlideIn {
    0% {
        opacity: 0;
        transform: translateY(-8px);
    }

    100% {
        opacity: 1;
        transform: translateY(0);
    }
}

#choices-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
    width: 100%;
}

/* ===== CHOICE BUTTONS ===== */
.choice-btn {
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius-sm);
    padding: 18px 16px;
    color: var(--text);
    font-family: var(--font);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: 0 4px 0 rgba(0, 0, 0, 0.2);
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 64px;
    position: relative;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
}

.choice-btn:hover {
    border-color: var(--blue);
    background: var(--bg-elevated);
    transform: translateY(-2px);
    box-shadow: 0 6px 0 rgba(0, 0, 0, 0.2);
}

.choice-btn:active {
    transform: translateY(2px);
    box-shadow: 0 2px 0 rgba(0, 0, 0, 0.2);
}

.choice-btn.selected {
    border-color: var(--blue);
    background: rgba(28, 176, 246, 0.15);
    box-shadow: 0 4px 0 rgba(28, 176, 246, 0.3);
}

.choice-btn.correct {
    border-color: var(--green);
    background: rgba(88, 204, 2, 0.15);
    box-shadow: 0 4px 0 rgba(88, 204, 2, 0.3);
    animation: correctPop 0.4s ease;
}

.choice-btn.incorrect {
    border-color: var(--red);
    background: rgba(255, 75, 75, 0.15);
    box-shadow: 0 4px 0 rgba(255, 75, 75, 0.3);
    animation: shake 0.4s ease;
}

.choice-btn.incorrect:not(:disabled):hover {
    border-color: var(--red);
    background: rgba(255, 75, 75, 0.25);
    transform: translateY(-2px);
    box-shadow: 0 6px 0 rgba(255, 75, 75, 0.3);
}

.choice-btn.incorrect:not(:disabled):active {
    transform: translateY(2px);
    box-shadow: 0 2px 0 rgba(255, 75, 75, 0.3);
}

.choice-btn.correct:not(:disabled):hover {
    border-color: var(--green);
    background: rgba(88, 204, 2, 0.25);
    transform: translateY(-2px);
    box-shadow: 0 6px 0 rgba(88, 204, 2, 0.3);
}

.choice-btn.correct:not(:disabled):active {
    transform: translateY(2px);
    box-shadow: 0 2px 0 rgba(88, 204, 2, 0.3);
}

.choice-btn:disabled {
    cursor: default;
    opacity: 0.6;
}

.choice-btn:disabled:hover {
    transform: none;
    box-shadow: 0 4px 0 rgba(0, 0, 0, 0.2);
}

.choice-btn.correct:disabled,
.choice-btn.incorrect:disabled {
    opacity: 1;
}

/* ===== FEEDBACK TOAST ===== */
#feedback-toast {
    width: 100%;
    padding: 18px 20px;
    border-radius: var(--radius);
    display: flex;
    align-items: flex-start;
    gap: 14px;
    z-index: 200;
    box-shadow: var(--shadow-lg);
    margin-top: 20px;
    opacity: 0;
    transform: translateY(10px);
    transition: opacity 0.35s ease, transform 0.35s ease;
}

#feedback-toast.visible {
    opacity: 1;
    transform: translateY(0);
}

#feedback-toast.correct {
    background: var(--green);
    color: #fff;
}

#feedback-toast.incorrect {
    background: var(--red);
    color: #fff;
}

#feedback-icon {
    font-size: 1.8rem;
    flex-shrink: 0;
    line-height: 1;
}

#feedback-title {
    font-weight: 800;
    font-size: 1.05rem;
    margin-bottom: 4px;
}

#feedback-explanation {
    font-size: 0.9rem;
    font-weight: 500;
    opacity: 0.92;
    line-height: 1.45;
}

/* ===== ACTION BAR ===== */
#action-bar {
    width: 100%;
    padding: 16px 0 0;
    display: flex;
    justify-content: center;
}

#continue-btn {
    width: 100%;
    max-width: 560px;
    padding: 16px;
    border: none;
    border-radius: var(--radius-sm);
    font-family: var(--font);
    font-size: 1.05rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 1px;
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: var(--shadow);
    color: #fff;
    background: var(--bg-elevated);
}

#continue-btn:disabled {
    opacity: 0.5;
    cursor: default;
}

#continue-btn.check {
    background: var(--blue);
    box-shadow: 0 4px 0 var(--blue-dark);
}

#continue-btn.check:hover:not(:disabled) {
    filter: brightness(1.1);
    transform: translateY(-1px);
    box-shadow: 0 5px 0 var(--blue-dark);
}

#continue-btn.next-correct {
    background: var(--green);
    box-shadow: 0 4px 0 var(--green-dark);
}

#continue-btn.next-incorrect {
    background: var(--red);
    box-shadow: 0 4px 0 var(--red-dark);
}

#continue-btn.next-correct:hover,
#continue-btn.next-incorrect:hover {
    filter: brightness(1.1);
    transform: translateY(-1px);
}

#continue-btn:active:not(:disabled) {
    transform: translateY(2px);
    box-shadow: 0 2px 0 rgba(0, 0, 0, 0.2);
}

/* ===== OVERLAY ===== */
#overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 500;
    padding: 20px;
}

#overlay-card {
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: 24px;
    padding: 48px 36px 36px;
    text-align: center;
    max-width: 400px;
    width: 100%;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
    animation: overlayIn 0.5s cubic-bezier(0.22, 1, 0.36, 1);
}

#overlay-icon {
    font-size: 4rem;
    margin-bottom: 16px;
}

#overlay-title {
    font-size: 1.6rem;
    font-weight: 900;
    margin-bottom: 8px;
}

#overlay-message {
    color: var(--text-muted);
    font-size: 1rem;
    margin-bottom: 28px;
    line-height: 1.5;
}

#overlay-btn {
    background: var(--green);
    color: #fff;
    border: none;
    border-radius: var(--radius-sm);
    padding: 14px 36px;
    font-family: var(--font);
    font-size: 1rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 1px;
    cursor: pointer;
    box-shadow: 0 4px 0 var(--green-dark);
    transition: all var(--transition);
}

#overlay-btn:hover {
    filter: brightness(1.1);
    transform: translateY(-1px);
}

#overlay-btn:active {
    transform: translateY(2px);
    box-shadow: 0 2px 0 var(--green-dark);
}

.overlay-secondary-btn {
    display: block;
    margin: 12px auto 0;
    background: transparent;
    border: 2px solid var(--bg-elevated);
    color: var(--text-muted);
    border-radius: var(--radius-sm);
    padding: 10px 24px;
    font-family: var(--font);
    font-size: 0.85rem;
    font-weight: 700;
    cursor: pointer;
    transition: all var(--transition);
}

.overlay-secondary-btn:hover {
    border-color: var(--blue);
    color: var(--text);
    background: var(--bg-elevated);
}

/* ===== HIDDEN UTILITY ===== */
.hidden {
    display: none !important;
}

/* ===== ANIMATIONS ===== */
@keyframes correctPop {
    0% {
        transform: scale(1);
    }

    30% {
        transform: scale(1.06);
    }

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

@keyframes shake {

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

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

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

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

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

@keyframes overlayIn {
    0% {
        opacity: 0;
        transform: scale(0.85) translateY(30px);
    }

    100% {
        opacity: 1;
        transform: scale(1) translateY(0);
    }
}

/* XP pop animation */
.xp-pop {
    position: fixed;
    top: 16px;
    right: 80px;
    font-size: 1.2rem;
    font-weight: 900;
    color: var(--gold);
    pointer-events: none;
    animation: xpFloat 1s ease forwards;
    z-index: 300;
}

@keyframes xpFloat {
    0% {
        opacity: 1;
        transform: translateY(0) scale(1);
    }

    100% {
        opacity: 0;
        transform: translateY(-40px) scale(1.3);
    }
}

/* Heart shake */
.heart-shake {
    animation: shake 0.4s ease;
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.04); }
    100% { transform: scale(1); }
}
.paused-pulse {
    animation: pulse 0.4s ease;
}

/* ===== RESPONSIVE ===== */
@media (max-width: 480px) {
    #problem-integral {
        font-size: 1.4rem;
    }

    #step-prompt {
        font-size: 1.05rem;
    }

    .choice-btn {
        padding: 14px 12px;
        font-size: 1rem;
        min-height: 56px;
    }

    #problem-card {
        padding: 22px 16px 18px;
    }
}

@media (min-width: 601px) {

    #top-bar,
    #app {
        padding-left: 32px;
        padding-right: 32px;
    }
}

/* ===== MENU SCREEN ===== */
#menu-screen {
    width: 100%;
    max-width: 540px;
    margin: 0 auto;
    padding: 60px 20px 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: 100vh;
    justify-content: center;
}

#menu-header {
    text-align: center;
    margin-bottom: 48px;
}

#menu-logo {
    font-size: 4rem;
    font-weight: 900;
    background: linear-gradient(135deg, var(--blue), var(--purple), var(--green));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 12px;
    line-height: 1;
}

#menu-title {
    font-size: 2rem;
    font-weight: 900;
    color: var(--text);
    margin-bottom: 8px;
}

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

#menu-cards {
    width: 100%;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.menu-card {
    width: 100%;
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius);
    padding: 24px 20px;
    display: flex;
    align-items: center;
    gap: 16px;
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: 0 4px 0 rgba(0, 0, 0, 0.2);
    color: var(--text);
    font-family: var(--font);
    text-align: left;
    position: relative;
    overflow: hidden;
}

.menu-card:hover {
    border-color: var(--blue);
    transform: translateY(-2px);
    box-shadow: 0 6px 0 rgba(0, 0, 0, 0.2);
}

.menu-card:active {
    transform: translateY(2px);
    box-shadow: 0 2px 0 rgba(0, 0, 0, 0.2);
}

.menu-card-icon {
    font-size: 2.2rem;
    flex-shrink: 0;
    width: 56px;
    height: 56px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-elevated);
    border-radius: 14px;
}

.menu-card-body {
    flex: 1;
    min-width: 0;
}

.menu-card-title {
    font-size: 1.05rem;
    font-weight: 800;
    margin-bottom: 4px;
}

.menu-card-desc {
    font-size: 0.85rem;
    color: var(--text-muted);
    font-weight: 500;
    line-height: 1.35;
}

.menu-card-badge {
    flex-shrink: 0;
    font-size: 0.7rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    color: var(--text-muted);
    background: var(--bg-elevated);
    padding: 4px 10px;
    border-radius: 999px;
}

/* ===== BACK BUTTON ===== */
#back-btn {
    flex-shrink: 0;
    width: 36px;
    height: 36px;
    border-radius: 50%;
    border: 2px solid var(--bg-elevated);
    background: transparent;
    color: var(--text-muted);
    font-size: 1.2rem;
    font-weight: 700;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
    -webkit-tap-highlight-color: transparent;
}

#back-btn:hover {
    border-color: var(--blue);
    color: var(--text);
    background: var(--bg-elevated);
}

/* ===== FORMULA REFERENCE BUTTON ===== */
#formula-ref-btn {
    flex-shrink: 0;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border: 2px solid rgba(28, 176, 246, 0.3);
    background: rgba(28, 176, 246, 0.08);
    font-size: 1.2rem;
    cursor: pointer;
    transition: all var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    -webkit-tap-highlight-color: transparent;
}

#formula-ref-btn:hover {
    background: rgba(28, 176, 246, 0.2);
    border-color: var(--blue);
    transform: scale(1.1);
}

/* ===== FORMULA REFERENCE OVERLAY ===== */
#formula-ref-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.75);
    backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 600;
    padding: 16px;
    animation: fadeIn 0.2s ease;
}

#formula-ref-card {
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: 20px;
    width: 100%;
    max-width: 720px;
    max-height: 85vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
    animation: overlayIn 0.3s cubic-bezier(0.22, 1, 0.36, 1);
}

#formula-ref-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 20px 24px;
    border-bottom: 1px solid var(--bg-elevated);
    flex-shrink: 0;
}

#formula-ref-header h2 {
    font-size: 1.3rem;
    font-weight: 800;
}

#formula-ref-close {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    border: none;
    background: var(--bg-elevated);
    color: var(--text-muted);
    font-size: 1.1rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
}

#formula-ref-close:hover {
    background: var(--red);
    color: #fff;
}

#formula-ref-table-wrap {
    overflow-y: auto;
    padding: 16px;
    flex: 1;
}

.formula-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.95rem;
}

.formula-table thead th {
    background: var(--bg-elevated);
    padding: 12px 10px;
    font-weight: 700;
    text-align: center;
    position: sticky;
    top: 0;
    z-index: 1;
    border-bottom: 2px solid rgba(255, 255, 255, 0.1);
}

.formula-table thead th em {
    display: block;
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--text-muted);
    margin-top: 2px;
}

.formula-table tbody tr {
    cursor: pointer;
    transition: opacity var(--transition), background var(--transition);
}

.formula-table tbody tr.inactive {
    opacity: 0.3;
}

.formula-table tbody tr.inactive:hover {
    opacity: 0.55;
}

.formula-table tbody td {
    padding: 10px;
    text-align: center;
    border-bottom: 1px solid rgba(255, 255, 255, 0.06);
    vertical-align: middle;
}

.formula-table tbody tr:hover {
    background: rgba(28, 176, 246, 0.06);
}

.formula-table tbody tr:nth-child(even) {
    background: rgba(255, 255, 255, 0.02);
}

.formula-table tbody tr:nth-child(even):hover {
    background: rgba(28, 176, 246, 0.06);
}

/* First column styling (Toggle Column) */
.formula-table th:first-child,
.formula-table td:first-child {
    width: 54px;
    min-width: 54px;
    max-width: 54px;
    padding-left: 6px;
    padding-right: 6px;
    text-align: center;
}

/* Custom Toggle Switch for Table */
.switch {
    position: relative;
    display: inline-block;
    width: 38px;
    height: 20px;
    vertical-align: middle;
    pointer-events: none; /* Make clicks pass through to the <tr> click handler */
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--bg-elevated);
    transition: var(--transition);
    border-radius: 20px;
    border: 1px solid rgba(255, 255, 255, 0.15);
}

.slider:before {
    position: absolute;
    content: "";
    height: 14px;
    width: 14px;
    left: 2px;
    bottom: 2px;
    background-color: var(--text-muted);
    transition: var(--transition);
    border-radius: 50%;
}

input:checked + .slider {
    background-color: var(--green);
    border-color: var(--green-dark);
}

input:checked + .slider:before {
    transform: translateX(20px);
    background-color: #fff;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

@media (max-width: 480px) {
    #menu-screen {
        padding: 40px 16px 30px;
    }

    #menu-title {
        font-size: 1.6rem;
    }

    #menu-logo {
        font-size: 3rem;
    }

    .menu-card {
        padding: 18px 16px;
        gap: 12px;
    }

    .menu-card-icon {
        width: 46px;
        height: 46px;
        font-size: 1.8rem;
    }

    .menu-card-badge {
        display: none;
    }

    .formula-table {
        font-size: 0.8rem;
    }

    .formula-table thead th,
    .formula-table tbody td {
        padding: 8px 6px;
    }

    #formula-ref-card {
        max-height: 90vh;
    }

    #formula-ref-header {
        padding: 16px;
    }

    #formula-ref-table-wrap {
        padding: 8px;
    }
}

/* ===== FORMULA MODE FILTER TOGGLE ===== */
.toggle-container {
    display: inline-flex;
    background: #0f191d;
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius-sm);
    padding: 3px;
    margin-top: 14px;
    gap: 2px;
    position: relative;
    z-index: 10;
    width: fit-content;
}

.toggle-btn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    font-family: var(--font);
    font-size: 0.78rem;
    font-weight: 700;
    padding: 6px 14px;
    border-radius: calc(var(--radius-sm) - 4px);
    cursor: pointer;
    transition: all var(--transition);
    white-space: nowrap;
}

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

.toggle-btn.active {
    background: var(--blue);
    color: #fff;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.25);
}

.menu-card:focus-visible {
    outline: none;
    border-color: var(--blue);
    box-shadow: 0 0 0 4px rgba(28, 176, 246, 0.4);
}

@media (max-width: 480px) {
    .toggle-container {
        display: flex;
        width: 100%;
        margin-top: 10px;
    }
    
    .toggle-btn {
        flex: 1;
        padding: 6px 4px;
        font-size: 0.7rem;
        text-align: center;
    }
}

/* ===== GRAPHING CANVAS ===== */
#problem-graph {
    margin-top: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100%;
    animation: fadeIn var(--transition);
}

#problem-graph canvas {
    background: rgba(15, 25, 29, 0.6);
    border-radius: var(--radius-sm);
    border: 1.5px solid var(--bg-elevated);
    max-width: 100%;
    display: block;
    box-shadow: inset 0 2px 8px rgba(0,0,0,0.4);
}

/* ===== FORMELARK INTERACTIVE COLUMNS/CELLS ===== */
.header-toggle-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 6px;
    justify-content: center;
}

.header-toggle-container .switch {
    pointer-events: auto; /* Allow header switches to be clicked directly */
}

.cell-content {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    position: relative;
}

/* Style individual td cells as inactive (dimmed) */
.formula-table tbody td.inactive {
    opacity: 0.3;
}

.formula-table tbody td.inactive:hover {
    opacity: 0.55;
}

/* Stasis snowflake badge styling */
.stasis-badge {
    color: var(--blue);
    font-size: 0.85rem;
    margin-left: 6px;
    cursor: help;
    display: inline-block;
    vertical-align: middle;
}

/* ===== MENU CARD TOGGLES LAYOUT ===== */
.menu-card-toggles {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
    margin-top: 14px;
}

.toggle-group {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.toggle-label {
    font-size: 0.72rem;
    font-weight: 800;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 0.5px;
}

/* ===== RULE BUILDER MODE ===== */
.rule-builder-grid {
    display: flex !important;
    flex-direction: column;
    gap: 16px;
    width: 100%;
}

.rule-builder-note {
    color: var(--text-muted);
    font-size: 0.92rem;
    line-height: 1.45;
    text-align: center;
    font-weight: 600;
}

.rule-choice-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 12px;
}

.rule-choice-btn,
.math-tile,
.skeleton-slot {
    font-family: var(--font);
    color: var(--text);
    cursor: pointer;
    transition: all var(--transition);
    -webkit-tap-highlight-color: transparent;
}

.rule-choice-btn {
    min-height: 74px;
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius-sm);
    background: var(--bg-card);
    box-shadow: var(--shadow);
    font-size: 1rem;
    font-weight: 850;
    padding: 16px 12px;
}

.rule-choice-btn:hover,
.rule-choice-btn.selected {
    border-color: var(--blue);
    background: rgba(28, 176, 246, 0.16);
    transform: translateY(-2px);
}

.rule-choice-btn.incorrect {
    border-color: var(--red);
    background: rgba(255, 75, 75, 0.16);
    animation: shake 0.4s ease;
}

.skeleton-board {
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius);
    padding: 18px;
    box-shadow: var(--shadow);
}

.skeleton-formula {
    min-height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    font-size: 1.1rem;
    font-weight: 800;
    margin-bottom: 14px;
}

.skeleton-slots {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 10px;
}

.skeleton-fixed {
    min-width: 34px;
    min-height: 52px;
    padding: 0 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    font-size: 1.15rem;
    font-weight: 900;
}

.skeleton-slot {
    min-width: 122px;
    min-height: 58px;
    border: 2px dashed rgba(28, 176, 246, 0.45);
    border-radius: var(--radius-sm);
    background: rgba(28, 176, 246, 0.08);
    padding: 12px 14px;
    font-size: 1rem;
    font-weight: 800;
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.03);
}

.skeleton-slot:hover {
    border-color: var(--blue);
    background: rgba(28, 176, 246, 0.16);
}

.skeleton-slot.filled {
    border-style: solid;
    border-color: var(--blue);
    background: rgba(28, 176, 246, 0.18);
}

.skeleton-slot.correct {
    border-color: var(--green);
    background: rgba(88, 204, 2, 0.18);
    animation: correctPop 0.35s ease;
}

.skeleton-slot.incorrect {
    border-color: var(--red);
    background: rgba(255, 75, 75, 0.18);
    animation: shake 0.4s ease;
}

.slot-label {
    color: var(--text-muted);
    font-size: 0.78rem;
    font-weight: 850;
    letter-spacing: 0.5px;
}

.tile-bank {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 10px;
}

.math-tile {
    min-height: 56px;
    border: 2px solid rgba(255, 255, 255, 0.08);
    border-radius: var(--radius-sm);
    background: #0f191d;
    padding: 11px 10px;
    font-size: 0.98rem;
    font-weight: 800;
    box-shadow: 0 3px 0 rgba(0, 0, 0, 0.28);
}

.math-tile:hover,
.math-tile.selected {
    border-color: var(--gold);
    background: rgba(255, 200, 0, 0.12);
    transform: translateY(-2px);
}

.math-tile:active {
    transform: translateY(1px);
    box-shadow: 0 1px 0 rgba(0, 0, 0, 0.28);
}

@media (max-width: 480px) {
    .rule-choice-grid,
    .tile-bank {
        grid-template-columns: 1fr;
    }

    .skeleton-board {
        padding: 14px;
    }

    .skeleton-slots {
        align-items: stretch;
    }

    .skeleton-slot {
        flex: 1 1 100%;
        min-width: 0;
    }

    .skeleton-fixed {
        flex: 0 0 auto;
        min-height: 34px;
    }
}

/* ===== ELEMENTS IDENTIFICATION LAYOUT ===== */
.elements-board {
    background: var(--bg-card);
    border: 2px solid var(--bg-elevated);
    border-radius: var(--radius);
    padding: 20px;
    box-shadow: var(--shadow);
}

.elements-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 14px;
}

.elements-row {
    display: flex;
    align-items: center;
    justify-content: flex-end;
    gap: 12px;
}

.elements-label {
    font-size: 1.1rem;
    font-weight: 800;
    color: var(--text-muted);
    min-width: 50px;
    text-align: right;
}

.element-slot {
    flex: 1;
    min-width: 100px !important;
}

@media (max-width: 480px) {
    .elements-grid {
        grid-template-columns: 1fr;
    }
}