:root {
    --app-bg: #f5f5f7;
    --app-bg-elevated: #fbfbfd;
    --panel: #ffffff;
    --panel-soft: rgba(255, 255, 255, .86);
    --ink: #1d1d1f;
    --muted: #6e6e73;
    --muted-strong: #515154;
    --line: rgba(0, 0, 0, .08);
    --line-strong: rgba(0, 0, 0, .14);
    --brand: #0066cc;
    --brand-hover: #0057b8;
    --brand-soft: #f1f7ff;
    --success: #1f8f4d;
    --warning: #b7791f;
    --danger: #c62828;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, .04);
    --shadow-md: 0 14px 36px rgba(0, 0, 0, .07);
    --shadow-lg: 0 28px 72px rgba(0, 0, 0, .11);
    --radius-sm: 8px;
    --radius-md: 8px;
    --radius-lg: 8px;
    --focus-ring: 0 0 0 4px rgba(0, 102, 204, .12);
}

* {
    box-sizing: border-box;
}

html {
    min-height: 100%;
    background: var(--app-bg);
}

body {
    min-height: 100vh;
    color: var(--ink);
    background:
        radial-gradient(circle at 50% -14%, #fff 0%, rgba(255, 255, 255, 0) 38%),
        linear-gradient(180deg, #fff 0%, #f5f5f7 34%, #f5f5f7 100%);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
    font-size: 16px;
    line-height: 1.65;
    letter-spacing: 0;
    text-rendering: optimizeLegibility;
    -webkit-font-smoothing: antialiased;
}

a {
    color: var(--brand);
    text-decoration: none;
}

a:hover {
    color: var(--brand-hover);
}

a,
.btn,
.panel,
.metric,
.answer-option,
.form-control,
.form-select,
.form-check-input,
.table tbody tr,
.quiz-nav-button,
.badge,
.paper-preview-light {
    transition:
        color .2s ease,
        background-color .2s ease,
        border-color .2s ease,
        box-shadow .2s ease,
        transform .2s ease,
        opacity .2s ease;
}

main.py-4 {
    padding-top: 34px !important;
    padding-bottom: 56px !important;
}

.container,
.container-fluid {
    --bs-gutter-x: 24px;
}

.container-fluid {
    max-width: 1440px;
}

.text-muted {
    color: var(--muted) !important;
}

.small,
small,
.form-text {
    color: var(--muted);
    font-size: 13px;
    line-height: 1.5;
}

hr {
    border-color: var(--line);
    opacity: 1;
}

.app-navbar,
.admin-navbar {
    position: sticky;
    top: 0;
    z-index: 30;
    min-height: 60px;
    border-bottom: 1px solid var(--line);
    background: rgba(255, 255, 255, .84);
    backdrop-filter: saturate(180%) blur(20px);
    box-shadow: var(--shadow-sm);
}

.app-navbar .navbar-brand,
.app-navbar .nav-link,
.admin-navbar .navbar-brand,
.admin-navbar .nav-link,
.admin-navbar .navbar-text {
    color: var(--ink);
}

.app-navbar .navbar-brand,
.admin-navbar .navbar-brand {
    font-size: 18px;
    font-weight: 760 !important;
}

.app-navbar .nav-link,
.admin-navbar .nav-link {
    color: var(--muted-strong);
    font-size: 15px;
    font-weight: 620;
}

.app-navbar .nav-link:hover,
.admin-navbar .nav-link:hover,
.app-navbar .navbar-brand:hover,
.admin-navbar .navbar-brand:hover {
    color: var(--brand);
}

.navbar-toggler {
    border-color: var(--line-strong);
    border-radius: var(--radius-sm);
}

.navbar-toggler:focus {
    box-shadow: var(--focus-ring);
}

.navbar-toggler-icon {
    filter: none;
}

.app-navbar .btn-outline-light,
.admin-navbar .btn-outline-light {
    color: var(--ink);
    border-color: var(--line-strong);
    background: rgba(255, 255, 255, .66);
}

.app-navbar .btn-outline-light:hover,
.admin-navbar .btn-outline-light:hover {
    color: #fff;
    border-color: var(--ink);
    background: var(--ink);
}

.panel {
    background: var(--panel-soft);
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-md);
    backdrop-filter: saturate(180%) blur(16px);
}

.panel:hover {
    border-color: rgba(0, 0, 0, .1);
}

.panel-pad {
    padding: 24px;
}

.section-title {
    margin-bottom: 16px;
    color: var(--ink);
    font-size: 23px;
    font-weight: 760;
    line-height: 1.25;
    letter-spacing: 0;
}

h1.section-title {
    font-size: clamp(28px, 3vw, 42px);
    line-height: 1.12;
}

h2.section-title {
    font-size: 22px;
}

.metric {
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 8px;
    min-height: 106px;
    padding: 18px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, .9);
    box-shadow: var(--shadow-sm);
}

.metric:hover {
    transform: translateY(-1px);
    box-shadow: 0 16px 34px rgba(0, 0, 0, .07);
}

.metric .value {
    color: var(--ink);
    font-size: 30px;
    font-weight: 780;
    line-height: 1.05;
    font-variant-numeric: tabular-nums;
}

.metric .label {
    order: -1;
    color: var(--muted);
    font-size: 13px;
    font-weight: 650;
}

.btn {
    min-height: 40px;
    border-radius: var(--radius-sm);
    font-weight: 680;
    letter-spacing: 0;
}

.btn-sm {
    min-height: 32px;
    border-radius: 7px;
    font-size: 13px;
}

.btn-lg {
    min-height: 48px;
    border-radius: var(--radius-md);
    font-size: 16px;
}

.btn-primary {
    border-color: var(--brand);
    background: var(--brand);
    box-shadow: 0 10px 22px rgba(0, 102, 204, .18);
}

.btn-primary:hover,
.btn-primary:focus {
    border-color: var(--brand-hover);
    background: var(--brand-hover);
    box-shadow: 0 14px 28px rgba(0, 102, 204, .24);
    transform: translateY(-1px);
}

.btn-outline-primary {
    color: var(--brand);
    border-color: rgba(0, 102, 204, .28);
    background: rgba(255, 255, 255, .72);
}

.btn-outline-primary:hover,
.btn-outline-primary:focus {
    color: #fff;
    border-color: var(--brand);
    background: var(--brand);
    box-shadow: 0 12px 24px rgba(0, 102, 204, .18);
    transform: translateY(-1px);
}

.btn-outline-secondary,
.btn-outline-warning,
.btn-outline-danger {
    background: rgba(255, 255, 255, .72);
}

.btn-outline-secondary {
    color: var(--muted-strong);
    border-color: var(--line-strong);
}

.btn-outline-secondary:hover {
    color: var(--ink);
    border-color: rgba(0, 0, 0, .24);
    background: #fff;
}

.btn-outline-warning {
    color: var(--warning);
    border-color: rgba(183, 121, 31, .28);
}

.btn-outline-danger {
    color: var(--danger);
    border-color: rgba(198, 40, 40, .26);
}

.form-label {
    color: var(--muted-strong);
    font-size: 14px;
    font-weight: 650;
}

.form-control,
.form-select,
textarea.form-control {
    min-height: 42px;
    border-color: var(--line);
    border-radius: var(--radius-sm);
    color: var(--ink);
    background-color: rgba(255, 255, 255, .92);
    box-shadow: inset 0 1px 1px rgba(0, 0, 0, .02);
}

.form-control-sm {
    min-height: 34px;
}

.form-control:focus,
.form-select:focus,
.form-check-input:focus {
    border-color: var(--brand);
    box-shadow: var(--focus-ring);
}

.form-control::placeholder {
    color: #a1a1a6;
}

.form-check-input {
    border-color: var(--line-strong);
}

.form-check-input:checked {
    border-color: var(--brand);
    background-color: var(--brand);
}

.alert {
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-sm);
}

.badge {
    border-radius: 999px;
    padding: .42em .68em;
    font-weight: 700;
    letter-spacing: 0;
}

.badge-soft {
    color: #0b4fa3;
    background: var(--brand-soft);
    border: 1px solid rgba(0, 102, 204, .16);
}

.table {
    --bs-table-bg: transparent;
    --bs-table-hover-bg: rgba(0, 0, 0, .025);
    margin-bottom: 0;
    color: var(--ink);
    border-color: var(--line);
}

.table thead th {
    color: var(--muted);
    border-bottom-color: var(--line);
    font-size: 13px;
    font-weight: 720;
    white-space: nowrap;
}

.table td,
.table th {
    vertical-align: middle;
    padding: 13px 12px;
}

.table-sm td,
.table-sm th {
    padding: 10px 8px;
}

.table tbody tr:hover {
    background: var(--bs-table-hover-bg);
}

.progress {
    overflow: hidden;
    border-radius: 999px;
    background: #eceef2;
    box-shadow: inset 0 1px 1px rgba(0, 0, 0, .03);
}

.progress-bar {
    border-radius: 999px;
    background: linear-gradient(90deg, var(--brand), #5aa7ff);
}

.modal-content {
    border: 1px solid var(--line);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
}

.modal-header,
.modal-footer {
    border-color: var(--line);
}

.answer-option {
    display: block;
    width: 100%;
    min-height: 50px;
    padding: 14px 16px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, .92);
    cursor: pointer;
}

.answer-option:hover {
    border-color: rgba(0, 102, 204, .35);
    background: #fff;
    box-shadow: 0 10px 24px rgba(0, 0, 0, .05);
}

.answer-option:has(input:checked) {
    border-color: rgba(0, 102, 204, .58);
    background: var(--brand-soft);
    box-shadow: 0 12px 26px rgba(0, 102, 204, .1);
}

.answer-option input {
    margin-right: 10px;
}

.question-stem {
    color: var(--ink);
    font-size: 17px;
    line-height: 1.82;
}

.question-prose {
    margin-bottom: 14px;
}

.question-prose p {
    margin: 0;
    white-space: pre-wrap;
}

.question-prose:last-child {
    margin-bottom: 0;
}

.question-heading {
    margin: 16px 0 10px;
    color: var(--ink);
    font-size: 18px;
    font-weight: 760;
    line-height: 1.45;
}

.question-list {
    margin: 12px 0;
    padding-left: 1.35rem;
}

.question-list li {
    margin: 5px 0;
}

.question-code {
    margin: 16px 0;
    padding: 18px;
    overflow-x: auto;
    border: 1px solid rgba(255, 255, 255, .08);
    border-radius: var(--radius-md);
    color: #edf4ff;
    background: #16181d;
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, .05);
    font-size: 15px;
    line-height: 1.7;
}

.question-code code {
    font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
    white-space: pre;
}

.inline-code {
    padding: 2px 6px;
    border: 1px solid rgba(0, 0, 0, .06);
    border-radius: 6px;
    background: #eef1f5;
    color: #1d1d1f;
    font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
    font-size: .92em;
}

.question-table-wrap {
    overflow-x: auto;
    margin: 16px 0;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: #fff;
}

.question-table {
    width: 100%;
    min-width: min(520px, 100%);
    border-collapse: collapse;
    background: #fff;
    font-size: 15px;
}

.question-table th,
.question-table td {
    padding: 11px 13px;
    border-bottom: 1px solid var(--line);
    text-align: left;
    vertical-align: top;
}

.question-table th {
    background: #f8f9fb;
    font-weight: 760;
}

.question-table tr:last-child td {
    border-bottom: 0;
}

.question-image {
    margin: 16px 0;
}

.question-image img {
    display: block;
    max-width: 100%;
    height: auto;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: #fff;
    box-shadow: var(--shadow-sm);
}

.option-text {
    white-space: pre-wrap;
}

.analysis-text {
    line-height: 1.8;
}

.analysis-rich {
    margin-top: 8px;
}

.analysis-rich .question-prose {
    margin-bottom: 8px;
}

.option-rich {
    display: inline-block;
    width: calc(100% - 38px);
    vertical-align: top;
    white-space: normal;
}

.option-rich .question-prose {
    margin: 0;
}

.option-rich .question-code {
    margin: 8px 0 0;
    padding: 12px;
    font-size: 14px;
}

.mjx-container {
    max-width: 100%;
    overflow-x: auto;
    overflow-y: hidden;
    padding: 2px 0;
}

.question-stem mjx-container[jax="CHTML"][display="true"],
.option-rich mjx-container[jax="CHTML"][display="true"],
.analysis-rich mjx-container[jax="CHTML"][display="true"] {
    margin: 12px 0;
}

.quiz-nav-button {
    width: 42px;
    height: 42px;
    padding: 0;
    border-radius: var(--radius-sm);
    font-weight: 700;
}

.quiz-nav-button.done {
    color: #0b4fa3;
    border-color: rgba(0, 102, 204, .22);
    background: var(--brand-soft);
}

.quiz-nav-button.current {
    color: #fff;
    border-color: var(--brand);
    background: var(--brand);
    box-shadow: 0 10px 20px rgba(0, 102, 204, .18);
}

.quiz-timer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    padding: 13px 15px;
    border: 1px solid rgba(0, 102, 204, .16);
    border-radius: var(--radius-md);
    background: var(--brand-soft);
}

.quiz-timer span {
    color: var(--muted);
    font-size: 14px;
    font-weight: 650;
}

.quiz-timer strong {
    color: #0b4fa3;
    font-size: 21px;
    font-weight: 760;
    font-variant-numeric: tabular-nums;
}

.paper-preview-light {
    min-height: 360px;
    padding: 28px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background:
        linear-gradient(90deg, rgba(0, 0, 0, .03) 1px, transparent 1px) 0 0 / 42px 42px,
        #fff;
    color: var(--ink);
    box-shadow: var(--shadow-lg);
}

.paper-preview-head {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    color: var(--muted);
    font-weight: 720;
}

.paper-preview h3 {
    margin: 28px 0 20px;
    color: var(--ink);
    font-size: 28px;
    font-weight: 800;
}

.paper-line {
    width: 72%;
    height: 10px;
    margin-bottom: 12px;
    border-radius: 999px;
    background: #dfe3ea;
}

.paper-line.long {
    width: 92%;
}

.paper-question-row {
    display: flex;
    align-items: center;
    gap: 12px;
    margin: 15px 0;
}

.paper-question-row span {
    display: grid;
    place-items: center;
    width: 34px;
    height: 34px;
    border-radius: var(--radius-sm);
    color: #fff;
    background: var(--brand);
    font-weight: 760;
}

.paper-question-row i {
    flex: 1;
    height: 12px;
    border-radius: 999px;
    background: #dfe3ea;
}

.paper-options {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-top: 18px;
}

.paper-options b {
    display: grid;
    place-items: center;
    min-height: 42px;
    border: 1px solid rgba(0, 102, 204, .18);
    border-radius: var(--radius-sm);
    color: var(--brand);
    background: rgba(255, 255, 255, .84);
}

.app-footer {
    color: var(--muted);
    padding: 28px 0;
}

.login-shell {
    min-height: calc(100vh - 116px);
    display: flex;
    align-items: center;
}

.login-panel {
    position: relative;
    width: 100%;
    max-width: 430px;
    margin: 0 auto;
    overflow: hidden;
}

.login-panel::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--brand), #86c5ff);
}

.bg-light {
    background: #f7f8fa !important;
}

.page-head {
    display: flex;
    align-items: flex-end;
    justify-content: space-between;
    gap: 20px;
    margin-bottom: 24px;
}

.page-head .section-title {
    margin-bottom: 4px;
}

.page-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.surface-list {
    display: grid;
    gap: 10px;
}

.surface-item {
    padding: 16px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, .74);
}

.surface-item:hover {
    border-color: rgba(0, 0, 0, .12);
    background: #fff;
}

.action-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 10px;
}

.paper-link {
    display: flex;
    flex-direction: column;
    gap: 6px;
    min-height: 78px;
    padding: 14px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    color: var(--ink);
    background: rgba(255, 255, 255, .74);
}

.paper-link:hover {
    color: var(--ink);
    border-color: rgba(0, 102, 204, .28);
    background: #fff;
    box-shadow: 0 12px 26px rgba(0, 102, 204, .08);
    transform: translateY(-1px);
}

.paper-link strong {
    font-size: 15px;
    line-height: 1.35;
}

.paper-link span {
    color: var(--muted);
    font-size: 13px;
}

.answer-summary {
    height: 100%;
    padding: 14px 16px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: #f7f8fa;
    color: var(--ink);
}

.answer-summary span {
    display: block;
    color: var(--muted);
    font-size: 13px;
    font-weight: 650;
}

.answer-summary strong {
    display: block;
    margin-top: 4px;
    font-size: 17px;
}

.filter-panel {
    align-items: center;
}

.filter-panel .form-control,
.filter-panel .form-select,
.filter-panel .btn {
    width: 100%;
}

.preview-question {
    padding: 16px;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, .78);
}

.preview-question + .preview-question {
    margin-top: 10px;
}

.paper-summary-row {
    padding: 14px 0;
    border-bottom: 1px solid var(--line);
}

.paper-summary-row:first-of-type {
    padding-top: 0;
}

.paper-summary-row:last-of-type {
    padding-bottom: 0;
    border-bottom: 0;
}

.table-question-text {
    max-width: 440px;
    color: var(--muted-strong);
    font-size: 14px;
    line-height: 1.55;
}

.admin-form-actions,
.student-form-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.login-panel .section-title {
    font-size: 30px;
}

.login-panel .login-subtitle {
    margin: -4px 0 22px;
    color: var(--muted);
}

@media (max-width: 992px) {
    .container-fluid {
        max-width: none;
    }

    .app-navbar,
    .admin-navbar {
        position: sticky;
    }

    .page-head {
        align-items: stretch;
        flex-direction: column;
    }
}

@media (max-width: 768px) {
    main.py-4 {
        padding-top: 24px !important;
        padding-bottom: 40px !important;
    }

    .panel-pad {
        padding: 18px;
    }

    .metric {
        min-height: 96px;
        padding: 16px;
    }

    .metric .value {
        font-size: 24px;
    }

    .section-title {
        font-size: 21px;
    }

    .question-stem {
        font-size: 16px;
    }

    .question-code {
        padding: 14px;
        font-size: 14px;
    }

    .table td,
    .table th {
        padding: 11px 10px;
    }

    .paper-preview-light {
        min-height: 320px;
        padding: 22px;
    }

    .action-grid {
        grid-template-columns: 1fr;
    }
}

@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        transition: none !important;
        animation: none !important;
        scroll-behavior: auto !important;
    }
}