* {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    margin: 0;
    font-family:
        Inter,
        system-ui,
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        sans-serif;
    background:
        radial-gradient(circle at top left, #19376f 0, transparent 30%),
        radial-gradient(circle at top right, #173c37 0, transparent 28%),
        #07101f;
    color: #edf4ff;
    line-height: 1.6;
}

a {
    color: inherit;
}

button,
select,
input,
textarea {
    font: inherit;
}

button,
.button {
    cursor: pointer;
}

.hero {
    min-height: 72vh;
    display: flex;
    align-items: center;
    border-bottom: 1px solid rgba(255,255,255,.1);
}

.hero-inner {
    width: min(1180px, 92%);
    margin: auto;
    padding: 80px 0;
}

.eyebrow,
.kicker,
.unit-number {
    text-transform: uppercase;
    letter-spacing: .15em;
    font-size: .8rem;
    font-weight: 800;
    color: #8bd7ff;
}

.hero h1 {
    font-size: clamp(4rem, 11vw, 9rem);
    line-height: .9;
    margin: 16px 0 25px;
}

.lead {
    max-width: 850px;
    font-size: clamp(1.2rem, 2vw, 1.65rem);
    color: #c9d8ed;
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    margin: 35px 0;
}

.button,
button {
    display: inline-block;
    border: 1px solid rgba(255,255,255,.2);
    background: rgba(255,255,255,.08);
    color: white;
    padding: 12px 18px;
    border-radius: 12px;
    text-decoration: none;
}

.primary {
    background: #e9f4ff;
    color: #07101f;
    font-weight: 800;
}

.stats {
    display: grid;
    grid-template-columns: repeat(4, minmax(100px, 1fr));
    max-width: 700px;
    gap: 12px;
    margin-top: 40px;
}

.stats div {
    padding: 18px;
    border-radius: 14px;
    background: rgba(255,255,255,.06);
    border: 1px solid rgba(255,255,255,.08);
}

.stats strong,
.stats span {
    display: block;
}

.stats strong {
    font-size: 1.7rem;
}

.stats span {
    color: #9fb0c8;
}

main {
    width: min(1180px, 92%);
    margin: auto;
    padding: 30px 0 100px;
}

.panel {
    margin: 30px 0;
    padding: clamp(24px, 4vw, 50px);
    border: 1px solid rgba(255,255,255,.09);
    border-radius: 24px;
    background: rgba(9,20,39,.82);
    backdrop-filter: blur(16px);
}

.section-heading h2 {
    margin: 6px 0 8px;
    font-size: clamp(2rem, 4vw, 3.4rem);
}

.section-heading p,
.unit p,
.large-text {
    color: #b8c8dc;
}

.teaching-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 14px;
    margin-top: 30px;
}

.teaching-grid article,
.unit,
.timeline article,
.practice-box,
.exam-launch,
.exam {
    padding: 22px;
    border-radius: 18px;
    background: rgba(255,255,255,.045);
    border: 1px solid rgba(255,255,255,.08);
}

.number {
    font-size: 2rem;
    font-weight: 900;
    color: #8bd7ff;
}

.units {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 18px;
    margin-top: 30px;
}

.unit h3 {
    font-size: 1.45rem;
    margin-bottom: 5px;
}

.unit ol {
    padding-left: 23px;
}

.unit li {
    margin: 8px 0;
    color: #c7d7eb;
}

.unit a {
    text-decoration: none;
}

.unit a:hover {
    text-decoration: underline;
    color: white;
}

.practice-box {
    margin-top: 30px;
}

.practice-controls,
.answer-row,
.hint-actions,
.level-row {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
    align-items: center;
}

select,
input,
textarea {
    border: 1px solid rgba(255,255,255,.15);
    color: white;
    background: #0b1729;
    border-radius: 10px;
    padding: 12px;
}

input {
    min-width: 260px;
}

textarea {
    width: 100%;
    min-height: 100px;
    resize: vertical;
}

.question {
    font-size: 1.5rem;
    font-weight: 700;
    padding: 28px 0;
}

.feedback {
    min-height: 35px;
    margin: 12px 0;
    font-weight: 800;
}

.correct {
    color: #86f7ae;
}

.incorrect {
    color: #ffd17c;
}

.hint {
    min-height: 50px;
    margin-top: 18px;
    padding: 16px;
    border-left: 3px solid #8bd7ff;
    background: rgba(139,215,255,.06);
}

.exam-launch {
    margin-top: 18px;
}

.exam {
    margin-top: 18px;
}

.exam-question {
    display: grid;
    grid-template-columns: 35px 1fr minmax(150px, 260px);
    gap: 10px;
    align-items: center;
    padding: 12px 0;
    border-bottom: 1px solid rgba(255,255,255,.06);
}

.exam-score {
    font-size: 2rem;
    font-weight: 900;
    margin: 25px 0 10px;
}

.tutor {
    margin-top: 25px;
}

.chat {
    max-height: 520px;
    overflow-y: auto;
    padding: 15px;
    background: rgba(0,0,0,.18);
    border-radius: 16px;
}

.bot-message,
.user-message {
    white-space: pre-wrap;
    padding: 15px;
    margin: 10px 0;
    border-radius: 14px;
}

.bot-message {
    background: rgba(139,215,255,.09);
}

.user-message {
    margin-left: 10%;
    background: rgba(255,255,255,.09);
}

.chat-input {
    margin-top: 12px;
}

.chat-input button {
    margin-top: 10px;
}

.timeline {
    display: grid;
    gap: 12px;
    margin-top: 30px;
}

.timeline h3 {
    color: #8bd7ff;
    margin-top: 0;
}

.lesson-header {
    width: min(1050px, 92%);
    margin: auto;
    padding: 65px 0 25px;
}

.lesson-header h1 {
    font-size: clamp(3rem, 7vw, 6rem);
    line-height: 1;
    margin: 15px 0;
}

.back {
    text-decoration: none;
    color: #a9c5e4;
}

.use-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.use-grid div {
    padding: 18px;
    border-radius: 12px;
    background: rgba(255,255,255,.05);
}

.generated-lesson {
    white-space: pre-wrap;
    margin-top: 25px;
    padding: 25px;
    background: rgba(0,0,0,.18);
    border-radius: 16px;
    min-height: 80px;
}

footer {
    text-align: center;
    padding: 40px;
    color: #71859f;
}

@media (max-width: 800px) {
    .teaching-grid,
    .units {
        grid-template-columns: 1fr;
    }

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

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

    .exam-question {
        grid-template-columns: 30px 1fr;
    }

    .exam-question input {
        grid-column: 2;
        min-width: 0;
        width: 100%;
    }
}