:root {
    --bg-color: #172038;
    --surface-color: rgba(23, 32, 56, 0.84);
    --surface-strong: rgba(37, 58, 94, 0.88);
    --text-color: #eef6f7;
    --muted-text: rgba(164, 221, 219, 0.72);
    --border-color: rgba(115, 190, 211, 0.18);
    --grid-color: rgba(115, 190, 211, 0.08);
    --tool-accent: #8c3a60;
    --axis-color: rgba(232, 246, 247, 0.7);
    --shadow-color: rgba(3, 9, 18, 0.34);
}

body.light-mode {
    --bg-color: #f7f0e4;
    --surface-color: rgba(255, 251, 245, 0.88);
    --surface-strong: rgba(246, 238, 224, 0.92);
    --text-color: #2f1e21;
    --muted-text: rgba(77, 43, 50, 0.7);
    --border-color: rgba(122, 72, 65, 0.18);
    --grid-color: rgba(122, 72, 65, 0.08);
    --tool-accent: #7a4841;
    --axis-color: rgba(47, 30, 33, 0.7);
    --shadow-color: rgba(75, 44, 29, 0.1);
}

* {
    box-sizing: border-box;
}

html,
body {
    margin: 0;
    min-height: 100%;
}

body {
    font-family: "Trebuchet MS", "Segoe UI", sans-serif;
    background:
        radial-gradient(circle at top left, rgba(115, 190, 211, 0.12), transparent 28%),
        var(--bg-color);
    color: var(--text-color);
}

body.modal-open {
    overflow: hidden;
}

button,
select,
a {
    font: inherit;
    color: inherit;
}

.page-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 20;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 1.25rem;
    pointer-events: none;
}

.header-actions {
    display: flex;
    gap: 0.75rem;
    pointer-events: auto;
}

.back-link,
.info-toggle,
.theme-toggle,
.info-close {
    pointer-events: auto;
    display: inline-flex;
    align-items: center;
    min-height: 2.8rem;
    padding: 0 1rem;
    border: 1px solid var(--border-color);
    border-radius: 999px;
    background: var(--surface-color);
    backdrop-filter: blur(16px);
    text-decoration: none;
    box-shadow: 0 14px 32px -24px var(--shadow-color);
    cursor: pointer;
    transition: transform 0.18s ease, border-color 0.18s ease;
}

.back-link:hover,
.info-toggle:hover,
.theme-toggle:hover,
.info-close:hover,
.back-link:focus-visible,
.info-toggle:focus-visible,
.theme-toggle:focus-visible,
.info-close:focus-visible {
    transform: translateY(-1px);
    border-color: rgba(115, 190, 211, 0.4);
}

.workspace {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 5.5rem 1rem 1rem;
}

.demo-shell {
    width: min(1280px, 100%);
}

.main-panel {
    display: grid;
    grid-template-columns: minmax(210px, 245px) minmax(0, 1fr) minmax(360px, 450px);
    gap: 1rem;
    align-items: stretch;
}

.sidebar {
    display: grid;
    gap: 0.75rem;
    align-content: start;
}

.controls,
.variables-panel {
    padding: 0.85rem 0.95rem;
    border: 1px solid var(--border-color);
    border-radius: 1.3rem;
    background: var(--surface-color);
    backdrop-filter: blur(18px);
    box-shadow: 0 24px 48px -34px var(--shadow-color);
}

.control-block {
    display: grid;
    gap: 0.35rem;
    min-width: 0;
}

.label {
    margin: 0;
    color: var(--muted-text);
    font-size: 0.76rem;
    font-weight: 700;
    letter-spacing: 0.16em;
    text-transform: uppercase;
}

.controls select {
    min-height: 2.8rem;
    padding: 0 0.9rem;
    border: 1px solid var(--border-color);
    border-radius: 0.9rem;
    background: var(--surface-strong);
    outline: none;
}

.sidebar select {
    min-height: 2.2rem;
    padding: 0 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 0.8rem;
    background: var(--surface-strong);
    color: var(--text-color);
    outline: none;
}

.formula-display {
    min-height: 2.6rem;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0 0.9rem;
    border: 1px solid var(--border-color);
    border-radius: 0.9rem;
    background: var(--surface-strong);
    color: var(--text-color);
    overflow-x: auto;
    overflow-y: hidden;
}

.integral-stack {
    display: grid;
    gap: 0.55rem;
}

.riemann-formula {
    min-height: 4.2rem;
    font-size: 1rem;
}

.integral-formula {
    min-height: 3.2rem;
    padding-top: 0.7rem;
    padding-bottom: 0.7rem;
    line-height: 1.45;
    font-size: 0.96rem;
}

.variables-panel {
    display: grid;
    gap: 0.65rem;
}

.compact-panel {
    min-height: 0;
}

.function-variables-panel {
    min-height: 23.5rem;
}

.transform-controls {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.7rem;
    align-content: start;
    min-height: 16.5rem;
}

.formula-display .MathJax {
    font-size: 1em !important;
}

.transform-field {
    display: grid;
    gap: 0.3rem;
}

.transform-field label {
    color: var(--muted-text);
    font-size: 0.8rem;
}

.slider-label {
    color: var(--muted-text);
    font-size: 0.8rem;
}

.transform-value {
    color: var(--text-color);
    font-size: 0.85rem;
}

.transform-field input,
.riemann-controls input[type="range"] {
    width: 100%;
    margin: 0;
    height: 1rem;
}

.transform-field input:focus-visible,
.controls select:focus-visible,
.riemann-controls select:focus-visible,
.riemann-controls input[type="number"]:focus-visible {
    border-color: rgba(115, 190, 211, 0.45);
}

.transform-hint,
.riemann-placeholder {
    margin: 0;
    grid-column: 1 / -1;
    color: var(--muted-text);
    font-size: 0.84rem;
    line-height: 1.35;
}

.riemann-controls {
    display: grid;
    gap: 0.7rem;
}

.riemann-controls select,
.riemann-controls input[type="number"] {
    min-height: 2.2rem;
    padding: 0 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 0.8rem;
    background: var(--surface-strong);
    color: var(--text-color);
    outline: none;
}

.bounds-block {
    gap: 0.3rem;
}

.checkbox-row {
    display: flex;
    align-items: center;
    gap: 0.55rem;
    color: var(--text-color);
    font-size: 0.9rem;
}

.checkbox-row input {
    margin: 0;
}

.canvas-panel {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0.85rem;
    border: 1px solid var(--border-color);
    border-radius: 1.5rem;
    background: var(--surface-color);
    box-shadow: 0 24px 48px -34px var(--shadow-color);
}

.canvas-frame {
    position: relative;
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
}

.canvas-zoom-controls {
    position: absolute;
    top: 1.1rem;
    right: 1.1rem;
    z-index: 2;
    display: grid;
    gap: 0.45rem;
}

.canvas-zoom-button {
    min-width: 2.3rem;
    min-height: 2.3rem;
    border: 1px solid var(--border-color);
    border-radius: 0.8rem;
    background: var(--surface-color);
    backdrop-filter: blur(12px);
    box-shadow: 0 12px 24px -18px var(--shadow-color);
    cursor: pointer;
}

.canvas-zoom-button:hover,
.canvas-zoom-button:focus-visible {
    border-color: rgba(115, 190, 211, 0.4);
}

.canvas-zoom-button:disabled {
    opacity: 0.45;
    cursor: default;
}

.controls {
    display: grid;
    gap: 0.75rem;
    align-content: start;
}

#riemann-canvas {
    display: block;
    width: 100%;
    height: 78vh;
    max-height: 840px;
    min-height: 600px;
    border-radius: 1rem;
    background: rgba(255, 255, 255, 0.02);
}

.info-modal[hidden] {
    display: none;
}

.info-modal {
    position: fixed;
    inset: 0;
    z-index: 30;
}

.info-backdrop {
    position: absolute;
    inset: 0;
    background: rgba(8, 14, 28, 0.58);
    backdrop-filter: blur(10px);
}

.info-panel {
    position: absolute;
    top: 50%;
    left: 50%;
    width: min(820px, calc(100% - 1.5rem));
    max-height: min(80vh, 900px);
    overflow: auto;
    transform: translate(-50%, -50%);
    padding: 1.25rem;
    border: 1px solid var(--border-color);
    border-radius: 1.5rem;
    background: var(--surface-color);
    box-shadow: 0 24px 64px -30px var(--shadow-color);
}

.info-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 1rem;
    margin-bottom: 1rem;
}

.info-header h2 {
    margin: 0;
    font-size: 1.8rem;
    line-height: 1.05;
}

.info-close {
    background: var(--surface-strong);
}

.info-content {
    display: grid;
    gap: 1rem;
}

.info-content section {
    padding: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 1rem;
    background: rgba(255, 255, 255, 0.02);
}

.info-content h3 {
    margin: 0 0 0.6rem;
}

.info-content p {
    margin: 0;
    line-height: 1.65;
    color: var(--muted-text);
}

@media (max-width: 760px) {
    .page-header {
        padding: 0.85rem;
    }

    .workspace {
        padding-top: 6rem;
    }

    .main-panel {
        grid-template-columns: 1fr;
    }

    .transform-controls {
        grid-template-columns: 1fr;
        min-height: 0;
    }

    #riemann-canvas {
        height: 460px;
        min-height: 460px;
    }

    .info-header {
        flex-direction: column;
    }
}