* {
    box-sizing: border-box;
}

:root {
    --bg: #edf2f7;
    --bg2: #dce7f2;
    --card: rgba(248, 251, 255, 0.92);
    --card-border: rgba(129, 157, 185, 0.34);
    --accent: #7bb6de;
    --accent-strong: #4f87b8;
    --text: #223447;
    --muted: #60758a;
    --success: #6baa85;
    --danger: #d9828c;
    --warning: #d8ac68;
    --shadow: 0 18px 40px rgba(96, 118, 142, 0.16);
}

body {
    margin: 0;
    min-height: 100vh;
    font-family: "Segoe UI", Roboto, Arial, sans-serif;
    color: var(--text);
    background:
        radial-gradient(circle at top left, rgba(123, 182, 222, 0.32), transparent 28%),
        radial-gradient(circle at top right, rgba(79, 135, 184, 0.22), transparent 34%),
        linear-gradient(180deg, var(--bg), var(--bg2));
}

a {
    color: #4f87b8;
}

.shell {
    width: 100%;
    max-width: none;
    margin: 0 auto;
    padding: 28px clamp(20px, 3vw, 40px) 40px;
}

.home-navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    margin-bottom: 18px;
    padding: 14px 16px;
    border-radius: 16px;
    border: 1px solid rgba(129, 157, 185, 0.28);
    background: rgba(244, 248, 252, 0.82);
    box-shadow: var(--shadow);
}

.home-navbar-brand {
    font-weight: 700;
    letter-spacing: .04em;
    color: #30465d;
}

.home-navbar-links {
    display: flex;
    align-items: center;
    gap: 10px;
}

.topbar {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 16px;
    margin-bottom: 28px;
}

.brand {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.kicker {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 6px 10px;
    border: 1px solid rgba(123, 182, 222, 0.34);
    border-radius: 999px;
    color: #426887;
    font-size: 12px;
    letter-spacing: .08em;
    text-transform: uppercase;
    background: rgba(123, 182, 222, 0.14);
}

.title {
    margin: 0;
    font-size: 34px;
    line-height: 1.1;
}

.subtitle {
    margin: 0;
    max-width: 780px;
    color: var(--muted);
}

.actions,
.inline-actions {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
    align-items: center;
}

.button,
.button-link,
.danger-button,
.ghost-button {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 11px 16px;
    border-radius: 12px;
    border: 1px solid rgba(129, 157, 185, .26);
    text-decoration: none;
    color: #f7fbff;
    cursor: pointer;
    font: inherit;
    font-weight: 600;
}

.button,
.button-link {
    background: linear-gradient(135deg, rgba(123, 182, 222, .82), rgba(79, 135, 184, .92));
    box-shadow: var(--shadow);
}

.ghost-button {
    background: rgba(233, 240, 247, .92);
    color: var(--text);
}

.danger-button {
    background: linear-gradient(135deg, rgba(217, 130, 140, .88), rgba(190, 118, 129, .94));
}

.grid {
    display: grid;
    gap: 20px;
}

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

.grid-2 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
}

.card,
.stat-card,
.question-card {
    background: var(--card);
    border: 1px solid var(--card-border);
    border-radius: 18px;
    box-shadow: var(--shadow);
    backdrop-filter: blur(10px);
}

.card,
.question-card {
    padding: 22px;
}

.stat-card {
    padding: 16px;
}

.stat-card span {
    display: block;
    color: var(--muted);
    font-size: 12px;
    letter-spacing: .06em;
    text-transform: uppercase;
}

.stat-card strong {
    display: block;
    margin-top: 8px;
    font-size: 28px;
}

.stat-card.status-pass {
    border-color: rgba(107, 170, 133, .44);
    background: rgba(107, 170, 133, .14);
}

.stat-card.status-fail {
    border-color: rgba(217, 130, 140, .4);
    background: rgba(217, 130, 140, .14);
}

.card-head {
    display: flex;
    justify-content: space-between;
    gap: 12px;
    align-items: flex-start;
    margin-bottom: 16px;
}

.section-title {
    margin: 0;
    font-size: 28px;
}

.section-note {
    margin: 8px 0 0;
    color: var(--muted);
    font-size: 14px;
}

.category-card {
    display: flex;
    flex-direction: column;
    gap: 14px;
    transition: transform .2s ease, border-color .2s ease, background .2s ease;
}

.category-card:hover {
    transform: translateY(-4px);
    border-color: rgba(123, 182, 222, .46);
}

.category-card.disabled {
    opacity: .72;
}

.category-icon {
    font-size: 42px;
}

.category-card h3,
.question-card h3 {
    margin: 0;
    font-size: 26px;
}

.category-card p,
.meta-text {
    margin: 0;
    color: var(--muted);
}

.category-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    margin-top: auto;
    flex-wrap: wrap;
}

.muted-note {
    color: var(--muted);
    font-size: 13px;
}

.pill {
    display: inline-flex;
    align-items: center;
    padding: 6px 10px;
    border-radius: 999px;
    background: rgba(233, 240, 247, .92);
    border: 1px solid rgba(129, 157, 185, .22);
    color: var(--muted);
    font-size: 12px;
}

.panel-stack {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.question-card {
    display: flex;
    flex-direction: column;
    gap: 18px;
}

.exam-card {
    display: flex;
    flex-direction: column;
    gap: 18px;
    margin-bottom: 20px;
}

.exam-card-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.exam-card-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 14px;
    flex-wrap: wrap;
    margin-top: 6px;
    padding-top: 6px;
}

.exam-card-note {
    flex: 1 1 320px;
}

.exam-start-button {
    margin-left: auto;
    padding: 14px 24px;
    min-height: 52px;
    font-size: 1rem;
    font-weight: 700;
}

.question-head {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
}

.question-text {
    margin: 0;
    font-size: 30px;
    line-height: 1.35;
}

.options {
    display: grid;
    gap: 14px;
}

.option-card {
    display: flex;
    gap: 12px;
    align-items: flex-start;
    padding: 16px;
    border-radius: 14px;
    border: 1px solid rgba(129, 157, 185, .22);
    background: rgba(236, 242, 248, .88);
}

.option-card input[type=radio] {
    margin-top: 4px;
}

.option-card.correct {
    border-color: rgba(107, 170, 133, .44);
    background: rgba(107, 170, 133, .16);
}

.option-card.wrong {
    border-color: rgba(217, 130, 140, .42);
    background: rgba(217, 130, 140, .14);
}

.feedback {
    padding: 16px 18px;
    border-radius: 16px;
    border: 1px solid rgba(129, 157, 185, .2);
}

.feedback.success {
    border-color: rgba(107, 170, 133, .44);
    background: rgba(107, 170, 133, .16);
}

.feedback.error {
    border-color: rgba(217, 130, 140, .42);
    background: rgba(217, 130, 140, .16);
}

.flash {
    margin-bottom: 18px;
    padding: 14px 16px;
    border-radius: 14px;
    border: 1px solid rgba(129, 157, 185, .22);
}

.flash.success {
    background: rgba(107, 170, 133, .16);
    color: #25503a;
}

.flash.error {
    background: rgba(217, 130, 140, .16);
    color: #6d3440;
}

.flash.warning {
    background: rgba(216, 172, 104, .18);
    color: #6a5228;
}

.form-grid {
    display: grid;
    gap: 16px;
}

.form-grid.two {
    grid-template-columns: repeat(2, minmax(0, 1fr));
}

.field {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

label {
    font-size: 13px;
    color: #41596f;
}

input[type=text],
input[type=password],
select,
textarea {
    width: 100%;
    padding: 12px 14px;
    border-radius: 12px;
    border: 1px solid rgba(129, 157, 185, .24);
    background: rgba(255, 255, 255, .88);
    color: var(--text);
    font: inherit;
}

textarea {
    min-height: 120px;
    resize: vertical;
}

.question-list {
    display: flex;
    flex-direction: column;
    gap: 14px;
}

.question-meta {
    display: flex;
    justify-content: space-between;
    gap: 12px;
    flex-wrap: wrap;
    color: var(--muted);
    font-size: 13px;
}

.option-list {
    display: grid;
    gap: 8px;
}

.option-row {
    padding: 10px 12px;
    border-radius: 12px;
    background: rgba(236, 242, 248, .88);
    border: 1px solid rgba(129, 157, 185, .18);
}

.option-row.correct {
    border-color: rgba(107, 170, 133, .42);
    background: rgba(107, 170, 133, .12);
}

.empty-state {
    padding: 22px;
    border-radius: 16px;
    border: 1px dashed rgba(129, 157, 185, .28);
    color: var(--muted);
    background: rgba(239, 245, 250, .88);
}

.center-card {
    max-width: 560px;
    margin: 80px auto 0;
}

.login-page {
    display: flex;
    align-items: center;
    justify-content: center;
}

.login-shell {
    width: 100%;
    max-width: 1160px;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 32px 20px;
}

.login-panel {
    width: min(100%, 980px);
    display: grid;
    grid-template-columns: minmax(0, 1.05fr) minmax(320px, 0.95fr);
    gap: 24px;
    align-items: stretch;
}

.login-showcase,
.login-card {
    height: 100%;
}

.login-showcase {
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    gap: 20px;
}

.login-copy {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.login-title {
    margin: 0;
    font-size: 42px;
    line-height: 1.08;
}

.login-text {
    margin: 0;
    color: var(--muted);
    font-size: 16px;
    line-height: 1.7;
}

.login-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.login-card {
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 20px;
}

.login-card-head {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.login-card-title {
    margin: 0;
    font-size: 28px;
}

.login-card-note {
    margin: 0;
    color: var(--muted);
    line-height: 1.6;
}

.login-form {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.login-actions {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
    align-items: center;
}

.hero {
    display: grid;
    grid-template-columns: minmax(0, 1.45fr) minmax(320px, 0.95fr);
    gap: 24px;
    align-items: stretch;
}

.hero-copy {
    display: flex;
    flex-direction: column;
    gap: 18px;
}

.hero-title {
    margin: 0;
    font-size: 46px;
    line-height: 1.08;
}

.hero-text {
    margin: 0;
    max-width: 760px;
    color: var(--muted);
    font-size: 17px;
    line-height: 1.7;
}

.hero-panel {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.hero-stats {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 12px;
}

.hero-note-card {
    padding: 18px;
    border-radius: 16px;
    border: 1px solid rgba(129, 157, 185, .22);
    background: rgba(236, 242, 248, .9);
}

.hero-note-card strong {
    display: block;
    margin-bottom: 8px;
    font-size: 18px;
}

.hero-note-card p {
    margin: 0;
    color: var(--muted);
    line-height: 1.6;
}

.hero-badges {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

.hero-badge,
.skill-chip {
    display: inline-flex;
    align-items: center;
    padding: 8px 12px;
    border-radius: 999px;
    border: 1px solid rgba(129, 157, 185, .22);
    background: rgba(236, 242, 248, .9);
    color: #3f5d79;
    font-size: 13px;
}

.homepage-section {
    margin-top: 26px;
}

.section-header {
    margin-bottom: 16px;
}

.homepage-topic-card,
.info-card {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.info-list {
    display: flex;
    flex-direction: column;
    gap: 14px;
}

.info-item strong {
    display: block;
    margin-bottom: 6px;
    font-size: 17px;
}

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

.skill-grid {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.exercise-toolbar {
    display: flex;
    justify-content: space-between;
    align-items: end;
    gap: 16px;
    margin-bottom: 20px;
    padding: 18px 22px;
}

.exercise-toolbar-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.exercise-toolbar-actions {
    align-items: flex-end;
}

.exercise-select {
    min-width: 180px;
    padding: 12px 14px;
    border-radius: 12px;
    border: 1px solid rgba(129, 157, 185, .24);
    background: rgba(255, 255, 255, .88);
    color: var(--text);
    font: inherit;
}

.java-exercise-card {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.java-exercise-card.is-complete {
    border-color: rgba(107, 170, 133, .42);
    background: rgba(107, 170, 133, .12);
}

.java-exercise-head {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 12px;
    flex-wrap: wrap;
}

.java-exercise-head h3 {
    margin: 10px 0 0;
    font-size: 24px;
}

.java-hint-box {
    padding: 16px 18px;
    border-radius: 16px;
    border: 1px solid rgba(216, 172, 104, .28);
    background: rgba(216, 172, 104, .16);
}

.java-hint-box strong {
    display: block;
    margin-bottom: 6px;
}

.java-hint-box p {
    margin: 0;
    color: #6a5228;
    line-height: 1.6;
}

.java-code-block {
    margin: 0;
    padding: 18px;
    overflow-x: auto;
    border-radius: 16px;
    border: 1px solid rgba(129, 157, 185, .22);
    background: rgba(232, 239, 246, .96);
    color: #223447;
    font-family: Consolas, "Courier New", monospace;
    font-size: 14px;
    line-height: 1.65;
    white-space: pre-wrap;
}

.java-draft {
    min-height: 180px;
    font-family: Consolas, "Courier New", monospace;
}

.java-solution {
    width: 100%;
}

.java-solution summary {
    cursor: pointer;
    color: #3f5d79;
    font-weight: 600;
    list-style: none;
}

.java-solution summary::-webkit-details-marker {
    display: none;
}

.java-solution summary::before {
    content: "▸";
    display: inline-block;
    margin-right: 8px;
    transition: transform .2s ease;
}

.java-solution[open] summary::before {
    transform: rotate(90deg);
}

.java-solution .java-code-block {
    margin-top: 14px;
}

@media (max-width: 920px) {
    .hero,
    .login-panel,
    .grid-3,
    .grid-2,
    .form-grid.two {
        grid-template-columns: 1fr;
    }

    .hero-title {
        font-size: 36px;
    }

    .hero-stats {
        grid-template-columns: 1fr;
    }

    .login-shell {
        align-items: stretch;
    }

    .login-title {
        font-size: 34px;
    }

    .home-navbar,
    .topbar {
        flex-direction: column;
        align-items: flex-start;
    }

    .exercise-toolbar {
        flex-direction: column;
        align-items: stretch;
    }

    .exercise-toolbar-actions {
        align-items: stretch;
    }
}