html, body {
    width: 100%;
    height: 100%;
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
    background: #2b3a4a;
}

:root {
    --lesson-font: 18px;
    --lesson-radius-s: 12px;
    --lesson-radius-m: 14px;
    --lesson-radius-l: 18px;
    --lesson-radius-xl: 24px;

    --lesson-border: rgba(0,0,0,0.10);
    --lesson-border-soft: rgba(0,0,0,0.08);
    --lesson-glass: rgba(255, 255, 255, 0.86);

    --lesson-primary-bg: rgba(77, 135, 255, 0.16);
    --lesson-primary-border: rgba(77, 135, 255, 0.28);
    --lesson-success-bg: rgba(55, 190, 120, 0.16);
    --lesson-success-border: rgba(55, 190, 120, 0.28);
    --lesson-danger-bg: rgba(255, 92, 92, 0.16);
    --lesson-danger-border: rgba(255, 92, 92, 0.28);

    --lesson-gap: 10px;
    --lesson-btn-h: 44px;
    --lesson-toolbar-h: 70px;
}

#stage {
    position: fixed;
    inset: 0;
    background:
        radial-gradient(circle at 18% 12%, rgba(255,255,255,0.18) 0%, rgba(255,255,255,0.06) 22%, rgba(255,255,255,0) 48%),
        radial-gradient(circle at 82% 18%, rgba(255,255,255,0.14) 0%, rgba(255,255,255,0.05) 18%, rgba(255,255,255,0) 44%),
        linear-gradient(165deg, #263445 0%, #2f4653 46%, #4b6a76 100%);
}

#stage::before {
    content: "";
    position: fixed;
    inset: 0;
    background:
        repeating-linear-gradient(135deg, rgba(255,255,255,0.035) 0px, rgba(255,255,255,0.035) 1px, rgba(255,255,255,0) 8px, rgba(255,255,255,0) 14px);
    opacity: 0.55;
    pointer-events: none;
}

#ui-root {
    position: fixed;
    inset: 0;
    z-index: 20;
    display: none;
    pointer-events: none;
    font-size: var(--lesson-font);
    line-height: 1.5;
}

#ui-root.is-visible {
    display: block;
}

.lesson-toast {
    position: fixed;
    left: 50%;
    top: calc(var(--lesson-toolbar-h) + 10px);
    transform: translateX(-50%);
    height: 44px;
    max-width: calc(100% - 24px);
    padding: 0 14px;
    border-radius: var(--lesson-radius-l);
    background: var(--lesson-glass);
    border: 1px solid var(--lesson-border-soft);
    backdrop-filter: blur(10px);
    display: flex;
    align-items: center;
    gap: 10px;
    pointer-events: none;
    opacity: 0;
    transition: opacity 120ms ease;
}

.lesson-toast.is-visible {
    opacity: 1;
}

.lesson-callouts {
    position: fixed;
    inset: 0;
    pointer-events: none;
    z-index: 21;
}

.lesson-callout-lines {
    position: fixed;
    inset: 0;
    pointer-events: none;
    z-index: 20;
}

.lesson-callout-lines line {
    stroke: rgba(255, 255, 255, 0.88);
    stroke-width: 3;
    stroke-linecap: round;
    filter: drop-shadow(0 2px 2px rgba(0,0,0,0.25));
}

.lesson-explain {
    position: fixed;
    top: 12px;
    left: 12px;
    width: 420px;
    max-width: calc(100% - 24px);
    border-radius: var(--lesson-radius-xl);
    background: rgba(255, 255, 255, 0.74);
    border: 1px solid var(--lesson-border);
    backdrop-filter: blur(10px);
    padding: 10px 12px 12px;
    display: none;
    pointer-events: auto;
    z-index: 22;
}

.lesson-explain.is-visible {
    display: block;
}

.lesson-explain__header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    margin-bottom: 6px;
}

.lesson-explain__title {
    font-weight: 900;
    font-size: 20px;
}

.lesson-explain__close {
    height: 44px;
    min-width: 44px;
    border-radius: 14px;
    border: 1px solid var(--lesson-border-soft);
    background: rgba(255,255,255,0.70);
    font-weight: 900;
    font-size: 22px;
}

.lesson-explain__body {
    font-size: 16px;
    line-height: 1.6;
    color: rgba(0,0,0,0.82);
}

.lesson-explain__actions {
    margin-top: 10px;
    display: none;
}

.lesson-explain__actions.is-visible {
    display: flex;
    justify-content: flex-end;
}

.lesson-btn.lesson-btn--tiny {
    height: 44px;
    padding: 0 14px;
    border-radius: var(--lesson-radius-m);
    background: rgba(255,255,255,0.70);
    border: 1px solid var(--lesson-border-soft);
    font-size: 16px;
    font-weight: 800;
}

.lesson-explain__hint {
    margin-top: 8px;
    font-size: 14px;
    color: rgba(0,0,0,0.60);
}

.lesson-callout {
    position: absolute;
    min-width: 140px;
    max-width: min(360px, calc(100vw - 24px));
    padding: 12px 14px;
    border-radius: var(--lesson-radius-xl);
    background: rgba(255, 255, 255, 0.35);
    border: 1px solid var(--lesson-border);
    backdrop-filter: blur(10px);
    color: rgba(0,0,0,0.84);
    transform: translate(-50%, -120%);
    opacity: 0;
    transition: opacity 120ms ease;
}

.lesson-callout.is-visible {
    opacity: 1;
}

.lesson-callout__title {
    font-weight: 800;
    font-size: 18px;
    margin-bottom: 6px;
}

.lesson-callout__body {
    font-size: 16px;
    line-height: 1.6;
}

.lesson-panel {
    position: fixed;
    left: 10px;
    right: 10px;
    bottom: 10px;
    border-radius: var(--lesson-radius-xl);
    background: var(--lesson-glass);
    border: 1px solid var(--lesson-border);
    backdrop-filter: blur(10px);
    pointer-events: auto;
    overflow: hidden;
}

.lesson-panel__handle {
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0 14px;
    gap: 10px;
    border-bottom: 1px solid var(--lesson-border-soft);
    user-select: none;
    position: relative;
}

.lesson-panel__toggle {
    height: 36px;
    min-width: 120px;
    border-radius: 0;
    border: 0;
    background: transparent;
    font-weight: 900;
    font-size: 30px;
    line-height: 1;
    color: rgba(0,0,0,0.70);
    transition: transform 90ms ease, color 120ms ease;
}

.lesson-panel__content {
    display: none;
    padding: 10px 14px 14px;
    gap: 10px;
}

.lesson-panel.is-open .lesson-panel__content {
    display: grid;
    grid-template-columns: 1fr;
}

.lesson-actions {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: var(--lesson-gap);
}

.lesson-actions.is-compact {
    grid-template-columns: repeat(3, minmax(0, 1fr));
}

.lesson-actionbar {
    width: min(560px, calc(100% - 12px));
    margin: 0 auto;
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: var(--lesson-gap);
    justify-content: center;
}

.lesson-btn {
    height: var(--lesson-btn-h);
    border-radius: var(--lesson-radius-m);
    border: 1px solid var(--lesson-border-soft);
    background: rgba(255,255,255,0.75);
    font-size: 16px;
    font-weight: 800;
    transition: transform 90ms ease, filter 120ms ease, background-color 120ms ease;
}

.lesson-btn.is-primary {
    background: var(--lesson-primary-bg);
    border-color: var(--lesson-primary-border);
}

.lesson-btn.is-danger {
    background: var(--lesson-danger-bg);
    border-color: var(--lesson-danger-border);
}

.lesson-btn.is-success {
    background: var(--lesson-success-bg);
    border-color: var(--lesson-success-border);
}

.lesson-btn:active,
.lesson-panel__toggle:active {
    transform: scale(0.96);
}

.lesson-btn:hover {
    filter: brightness(1.02);
}

.lesson-btn:disabled {
    opacity: 0.45;
    filter: grayscale(0.15);
    cursor: not-allowed;
    transform: none;
}

.lesson-btn.is-disabled:active {
    transform: none;
}

.lesson-kpi {
    display: grid;
    grid-template-columns: 1fr;
    gap: 10px;
    padding-top: 10px;
}

.lesson-kpi__row {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: center;
    justify-content: space-between;
}

.lesson-kpi__item {
    font-size: 18px;
    font-weight: 900;
    padding: 8px 10px;
    border-radius: var(--lesson-radius-s);
    border: 1px solid var(--lesson-border-soft);
    background: rgba(255,255,255,0.65);
    min-height: 44px;
    display: inline-flex;
    align-items: center;
}

@media (max-width: 640px) {
    .lesson-actionbar {
        width: calc(100% - 4px);
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}

@media (max-width: 520px) {
    .lesson-callouts,
    .lesson-callout,
    .lesson-callout-lines {
        display: none !important;
    }
}