:root {
    --navy: #2c3e50;
    --softgray: #ecf0f1;
    --teal: #1abc9c;
    --gold: #f1c40f;
    --slate: #7f8c8d;
    --coral: #e74c3c;
    --white: #ffffff;
    --gray-100: #f7fafc;
    --gray-200: #edf2f7;
    --gray-300: #e2e8f0;
    --max-width: 1120px;
    --container-pad: 16px;
    --radius: 10px;
    --shadow-sm: 0 6px 18px rgba(0, 0, 0, 0.06);
    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.06);
}

* {
    box-sizing: border-box;
}

html,
body {
    height: 100%;
}

body {
    margin: 0;
    font-family: "Montserrat", system-ui, -apple-system, "Segoe UI", Roboto,
        "Helvetica Neue", Arial;
    color: var(--navy);
    background: linear-gradient(135deg, #ecf0f1 0%, #d6dbdf 100%);
    padding: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Responsive container */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 16px;
}

li {
    line-height: 2;
    /* Sets line height to 1.5 times the font size */
}

/* Page header */
.page-header {
    text-align: center;
    color: var(--navy);
    padding: 1rem;
    position: relative;
}

.header-grid {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    /* left spacer | center title (auto) | right actions */
    align-items: center;
    gap: 12px;
    padding: 8px 0;
}

/* center the title inside the middle column */
.page-title {
    margin: 0;
    justify-self: center;
    /* ensures exact centering of the title cell */
    font-size: clamp(20px, 2.2vw, 28px);
    font-weight: 700;
}

/* position actions at the end of the right column */
.header-actions {
    justify-self: end;
}

.header-left {
    justify-self: start;
}

/* mobile: stack nicely */
@media (max-width: 767px) {
    .header-grid {
        grid-template-columns: 1fr;
        /* stack everything */
        grid-auto-flow: row;
        text-align: left;
    }

    .page-title {
        justify-self: start;
    }

    .header-actions {
        justify-self: start;
        width: 100%;
        margin-top: 8px;
    }

    .quiz-btn {
        width: 100%;
        max-width: 420px;
    }
}


/* Experiment area */
.experiment-area {
    background: var(--gray-100);
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 24px;
}

.cols {
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.sim-area {
    background: var(--softgray);
    border-radius: 8px;
    padding: 12px;
    position: relative;
    overflow: hidden;
    height: clamp(280px, 50vw, 400px);
}

.track {
    position: absolute;
    left: 0;
    right: 0;
    height: 6px;
    background: linear-gradient(90deg, #d5d5d5, #bfbfbf);
    bottom: 100px;
}

.distance-markers {
    position: absolute;
    left: 0;
    right: 0;
    display: flex;
    justify-content: space-between;
    padding: 0 16px;
}

.marker {
    display: flex;
    flex-direction: column;
    align-items: center;
    font-size: 12px;
    color: var(--navy);
}

.marker-line {
    background: var(--slate);
    width: 2px;
}

.marker-line.major {
    height: 16px;
    background: var(--navy);
    width: 4px;
}

.marker-line.minor {
    height: 8px;
    width: 1px;
}

.finish-line {
    position: absolute;
    right: 16px;
    width: 4px;
    height: 64px;
    background: repeating-linear-gradient(0deg,
            #000,
            #000 10px,
            #fff 10px,
            #fff 20px);
    border-radius: 2px;
}

.cart-container {
    position: absolute;
}

.cart {
    position: relative;
}

.cart-svg {
    display: block;
}

/* Force arrow */
.force-arrow {
    position: absolute;
    left: 100%;
    top: 35%;
    transform: translateY(-50%);
    display: flex;
    align-items: center;
}

.force-arrow-line {
    height: 4px;
    background: var(--coral);

    width: 80px;
    transition: width 0.18s ease;
}

.force-arrow-head {
    width: 0;
    height: 0;
    border-top: 6px solid transparent;
    border-bottom: 6px solid transparent;
    border-left: 10px solid var(--coral);
}

/* Timer / velocity badges */
.badge {
    position: absolute;
    background: rgba(255, 255, 255, 0.96);
    border-radius: 6px;
    padding: 6px 10px;
    font-size: 13px;
    font-weight: 600;
    box-shadow: var(--shadow-xs);
}

.timer {
    left: 16px;
    top: 16px;
}

.velocity {
    right: 16px;
    top: 16px;
}

/* Controls */
.controls {
    background: white;
    border-radius: 8px;
    padding: 16px;
    box-shadow: var(--shadow-sm);
}

.control-group {
    margin-bottom: 18px;
}

.label {
    display: block;
    margin-bottom: 6px;
    font-size: 14px;
    color: var(--slate);
    font-weight: 600;
}

.range-row {
    display: flex;
    align-items: center;
    gap: 12px;
}

.range {
    flex: 1;
}

.value {
    display: inline-block;
    padding: 6px 8px;
    border-radius: 6px;
    background: rgba(26, 188, 156, 0.12);
    color: var(--teal);
    min-width: 64px;
    text-align: center;
    font-weight: 700;
}

.value.coral {
    background: rgba(231, 76, 60, 0.12);
    color: var(--coral);
}

/* Button styles */
.teal-btn {
    background-color: rgba(26, 188, 156, 0.8);
    color: white;
}

.teal-btn:hover {
    background-color: rgba(26, 188, 156, 0.7);
    transform: translateY(-2px);
}

.gold-btn {
    background-color: rgba(241, 196, 15, 1);
    color: var(--navy);
    opacity: 0.9;
}

.gold-btn:hover {
    background-color: rgba(241, 196, 15, 0.5);
    transform: translateY(-10%);
    opacity: .98;
}

.coral-btn {
    background-color: rgba(231, 76, 60, 0.8);
    color: white;
}

.coral-btn:hover {
    background-color: rgba(231, 76, 60, 0.7);
}

.navy-btn {
    background-color: rgba(44, 62, 80, 0.8);
    color: white;
}

.navy-btn:hover {
    background-color: rgba(44, 62, 80, 0.7);
    transform: translateY(-2px);
}

.teal-btn:active,
.gold-btn:active,
.coral-btn:active,
.navy-btn:active {
    transform: translateY(1px);
    opacity: 0.95;
}

.button-stack {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-top: 24px;
}

.btn {
    display: inline-block;
    padding: 0.5rem 1rem;
    border-radius: 0.375rem;
    font-weight: 500;
    text-decoration: none;
    text-align: center;
    transition: all 0.2s;
    cursor: pointer;
    border: 1px solid transparent;
    width: auto;
    font-size: 16px;
    font-weight: 600;
    padding: 12px 24px;
}




.btn.small {
    padding: 6px 10px;
    font-size: 13px;
}

.btn.soft {
    background: var(--softgray);
    color: var(--slate);
}

/* Panels */
.panel {
    margin-top: 24px;
    background: white;
    border-radius: 8px;
    padding: 16px;
    box-shadow: var(--shadow-sm);
}

.panel h3 {
    margin: 0 0 12px 0;
    font-size: 18px;
}

.panel .panel-body {
    color: var(--navy);
}

.panel ol,
.panel ul {
    margin: 8px 0 0 20px;
}

/* Results table */
.table-wrap {
    overflow-x: auto;
}

.results-table {
    width: 100%;
    border-collapse: collapse;
    background: white;
    border: 1px solid var(--softgray);
}

.results-table th,
.results-table td {
    border: 1px solid var(--softgray);
    padding: 8px;
    text-align: left;
}

.results-table thead tr {
    background: var(--softgray);
}

.results-table th {
    font-weight: 700;
}

/* Formula / worksheet */
.formula {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 12px;
}

.formula-pill {
    padding: 6px 10px;
    border-radius: 6px;
    font-weight: 700;
}

.formula-pill.teal {
    background: rgba(26, 188, 156, 0.12);
    color: var(--teal);
}

.formula-pill.gold {
    background: rgba(241, 196, 15, 0.12);
    color: var(--navy);
}

.formula-pill.coral {
    background: rgba(231, 76, 60, 0.12);
    color: var(--coral);
}

/* Range input styling for modern browsers */
input[type="range"] {
    -webkit-appearance: none;
    appearance: none;
    height: 6px;
    background: transparent;
    touch-action: none;
}

input[type="range"]:focus {
    outline: none;
}

input[type="range"]::-webkit-slider-runnable-track {
    height: 6px;
    background: linear-gradient(90deg, #d0d0d0, #bdbdbd);
    border-radius: 6px;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--navy);
    margin-top: -11px;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
}

input[type="range"]::-moz-range-track {
    height: 6px;
    background: linear-gradient(90deg, #d0d0d0, #bdbdbd);
    border-radius: 6px;
}

input[type="range"]::-moz-range-thumb {
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--navy);
    border: none;
}

/* Accessibility focus states */
a:focus,
button:focus,
input:focus {
    outline: 3px solid rgba(26, 188, 156, 0.18);
    outline-offset: 2px;
}

/* Small utilities */
.text-center {
    text-align: center;
}

.mt-4 {
    margin-top: 16px;
}

.mb-4 {
    margin-bottom: 16px;
}

.p-4 {
    padding: 16px;
}

/* Responsive */
@media (min-width: 768px) {
    body {
        padding: 24px;
    }

    .container {
        padding: 0;
    }

    .cols {
        flex-direction: row;
    }

    .sim-area {
        flex: 2;
        margin-right: 24px;
    }

    .controls {
        flex: 1;
    }

    .page-title {
        font-size: 32px;
    }
}

@media (max-width: 767px) {
    .container {
        padding: 0 12px;
    }
}

/* ---------- data table styles (from your snippet) ---------- */
.data-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
    background: white;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.data-table th,
.data-table td {
    padding: 12px;
    text-align: center;
    border-bottom: 1px solid #e2e8f0;
}

.data-table th {
    background: #4a5568;
    color: white;
    font-weight: 600;
}

.data-table tr:hover {
    background: #f7fafc;
}

/* row for incomplete trial sets */
tr.incomplete {
    opacity: 0.9;
    background-color: #fff5f5;
}

tr.incomplete td {
    border-bottom: 2px dashed #e53e3e;
}

/* status badges (if you want to use them elsewhere) */
.status {
    text-align: center;
    padding: 10px;
    border-radius: 5px;
    margin: 10px 0;
    font-weight: 600;
}

.status.ready {
    background: #c6f6d5;
    color: #22543d;
}

.status.running {
    background: #fed7d7;
    color: #742a2a;
}

.speed-input {
    width: 90px;
    padding: 6px 8px;
    border: 1px solid #cbd5e0;
    border-radius: 4px;
    text-align: center;
    transition: all 0.18s ease;
    font-weight: 600;
}

.speed-input.correct {
    background-color: #c6f6d5;
    border-color: #48bb78;
}

.speed-input.incorrect {
    background-color: #fed7d7;
    border-color: #f56565;
}

.validation-icon {
    font-size: 18px;
    display: inline-block;
    width: 28px;
    height: 28px;
    text-align: center;
    line-height: 28px;
    border-radius: 50%;
    vertical-align: middle;
    margin-left: 6px;
}

.validation-icon.correct {
    color: #48bb78;
    background-color: #f0fff4;
}

.validation-icon.incorrect {
    color: #e53e3e;
    background-color: #fff5f5;
}

/* small action button */
.row-delete {
    background: none;
    border: 0;
    cursor: pointer;
    color: #e53e3e;
    font-size: 16px;
}