* {
    box-sizing: border-box;
}


:root {

    --bg: #f6f8fc;

    --surface: #ffffff;

    --text: #172033;

    --muted: #687287;

    --primary: #5b5ce2;

    --primary-dark: #4748c6;

    --border: #e4e7ef;

    --success: #15803d;

    --success-bg: #ecfdf3;

    --danger: #dc2626;

    --danger-bg: #fef2f2;

}


html {
    scroll-behavior: smooth;
}


body {

    margin: 0;

    background: var(--bg);

    color: var(--text);

    font-family:
        Inter,
        ui-sans-serif,
        system-ui,
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        sans-serif;

}


/* =========================
   NAVBAR
========================= */

.navbar {

    height: 72px;

    padding: 0 7%;

    display: flex;

    align-items: center;

    justify-content: space-between;

    background: rgba(255, 255, 255, .94);

    border-bottom: 1px solid var(--border);

    position: sticky;

    top: 0;

    z-index: 20;

    backdrop-filter: blur(12px);

}


.logo {

    color: var(--text);

    text-decoration: none;

    display: flex;

    align-items: center;

    font-size: 20px;

    font-weight: 800;

}


.logo span {

    width: 34px;

    height: 34px;

    display: grid;

    place-items: center;

    margin-right: 9px;

    border-radius: 10px;

    color: white;

    background: var(--primary);

}


.nav-links {

    display: flex;

    gap: 8px;

}


.nav-links a {

    color: var(--muted);

    text-decoration: none;

    padding: 10px 14px;

    border-radius: 10px;

    font-weight: 650;

    transition: .15s;

}


.nav-links a:hover,
.nav-links a.active {

    color: var(--primary);

    background: #eef0ff;

}


/* =========================
   ALGEMEEN
========================= */

.badge {

    display: inline-block;

    color: var(--primary);

    background: #eef0ff;

    border-radius: 999px;

    padding: 7px 12px;

    font-size: 13px;

    font-weight: 800;

}


.button {

    border: 0;

    display: inline-flex;

    align-items: center;

    justify-content: center;

    gap: 15px;

    padding: 14px 19px;

    border-radius: 12px;

    background: var(--primary);

    color: white;

    text-decoration: none;

    font-weight: 800;

    font-size: 15px;

    cursor: pointer;

    transition: .2s;

}


.button:hover {

    background: var(--primary-dark);

    transform: translateY(-1px);

}


.button.secondary {

    background: #eceef5;

    color: var(--text);

}


.button.secondary:hover {

    background: #e0e3ed;

}


/* =========================
   HOME
========================= */

.hero {

    min-height: 590px;

    padding: 80px 7%;

    display: grid;

    grid-template-columns: 1.1fr .9fr;

    gap: 70px;

    align-items: center;

    background:
        radial-gradient(
            circle at 85% 30%,
            #e9eaff 0,
            transparent 35%
        );

}


.hero h1 {

    font-size: clamp(42px, 6vw, 70px);

    line-height: 1.02;

    margin: 18px 0;

    letter-spacing: -2.5px;

}


.hero h1 span {

    display: block;

    color: var(--primary);

}


.hero-content p {

    max-width: 650px;

    color: var(--muted);

    font-size: 18px;

    line-height: 1.7;

}


.hero-content .button {

    margin-top: 20px;

}


.formula-card {

    background: var(--surface);

    border: 1px solid var(--border);

    border-radius: 24px;

    padding: 35px;

    box-shadow:
        0 20px 60px rgba(35, 42, 80, .08);

}


.formula-label {

    color: var(--muted);

    font-size: 13px;

    font-weight: 800;

    text-transform: uppercase;

}


.formula {

    margin: 25px 0 12px;

    font-size: 29px;

    font-weight: 850;

}


.formula span {

    color: var(--primary);

}


.formula-card p {

    color: var(--muted);

}


.mini-formulas {

    display: grid;

    grid-template-columns: repeat(3, 1fr);

    gap: 10px;

    margin-top: 30px;

}


.mini-formulas div {

    padding: 14px;

    border: 1px solid var(--border);

    border-radius: 14px;

}


.mini-formulas b {

    display: block;

    font-size: 21px;

}


.mini-formulas small {

    color: var(--muted);

}


.info-section {

    max-width: 1200px;

    margin: 0 auto;

    padding: 80px 7%;

}


.section-title h2 {

    font-size: 35px;

    margin: 12px 0 30px;

}


.cards {

    display: grid;

    grid-template-columns: repeat(3, 1fr);

    gap: 18px;

}


.info-card {

    background: white;

    border: 1px solid var(--border);

    border-radius: 18px;

    padding: 25px;

}


.icon {

    width: 44px;

    height: 44px;

    display: grid;

    place-items: center;

    border-radius: 12px;

    background: #eef0ff;

    color: var(--primary);

    font-size: 20px;

    font-weight: 900;

}


.info-card h3 {

    font-size: 23px;

    margin-bottom: 7px;

}


.info-card p {

    color: var(--muted);

    line-height: 1.65;

}


/* =========================
   OEFENPAGINA
========================= */

.practice-page {

    max-width: 1100px;

    margin: 0 auto;

    padding: 55px 25px 100px;

}


.practice-header {

    display: flex;

    align-items: end;

    justify-content: space-between;

    gap: 30px;

}


.practice-header h1 {

    font-size: 50px;

    margin: 12px 0 6px;

    letter-spacing: -1.5px;

}


.practice-header p {

    color: var(--muted);

    margin: 0;

}


.score-box {

    min-width: 120px;

    padding: 13px 20px;

    background: white;

    border: 1px solid var(--border);

    border-radius: 15px;

    text-align: center;

}


.score-box span {

    display: block;

    color: var(--muted);

    font-size: 12px;

}


.score-box strong {

    font-size: 22px;

}


/* =========================
   INSTELLINGEN
========================= */

.settings-card {

    margin: 35px 0 18px;

    padding: 22px;

    display: grid;

    grid-template-columns: 1fr 1fr;

    gap: 30px;

    background: white;

    border: 1px solid var(--border);

    border-radius: 18px;

}


.settings-column h2 {

    margin: 0 0 5px;

    font-size: 18px;

}


.settings-description {

    color: var(--muted);

    margin: 0 0 15px;

    font-size: 13px;

}


/* CHECKBOX */

.checkbox-option {

    display: flex;

    align-items: center;

    gap: 12px;

    padding: 12px;

    margin-top: 7px;

    border: 1px solid var(--border);

    border-radius: 12px;

    cursor: pointer;

    transition: .15s;

}


.checkbox-option:hover {

    background: #f7f7ff;

    border-color: #cfd1ff;

}


.checkbox-option input {

    display: none;

}


.custom-checkbox {

    width: 21px;

    height: 21px;

    position: relative;

    flex-shrink: 0;

    border: 2px solid #cfd3df;

    border-radius: 6px;

}


.checkbox-option input:checked + .custom-checkbox {

    background: var(--primary);

    border-color: var(--primary);

}


.checkbox-option input:checked + .custom-checkbox::after {

    content: "✓";

    position: absolute;

    left: 3px;

    top: -1px;

    color: white;

    font-size: 14px;

    font-weight: bold;

}


.checkbox-text {

    display: flex;

    flex-direction: column;

}


.checkbox-text strong {

    font-size: 15px;

}


.checkbox-text small {

    color: var(--muted);

    margin-top: 2px;

}


/* RADIO */

.radio-option {

    display: flex;

    align-items: flex-start;

    gap: 10px;

    padding: 9px 0;

    cursor: pointer;

}


.radio-option input {

    width: 17px;

    height: 17px;

    margin-top: 2px;

    accent-color: var(--primary);

}


.radio-option span {

    display: flex;

    flex-direction: column;

}


.radio-option strong {

    font-size: 14px;

}


.radio-option small {

    color: var(--muted);

    font-size: 12px;

    margin-top: 2px;

    line-height: 1.4;

}


.settings-button {

    width: 100%;

    margin-top: 12px;

}


.selection-error {

    padding: 13px 16px;

    margin-bottom: 18px;

    color: var(--danger);

    background: var(--danger-bg);

    border-radius: 12px;

    font-weight: 650;

}


/* =========================
   VRAAG
========================= */

.question-card {

    background: white;

    border: 1px solid var(--border);

    border-radius: 22px;

    padding: 30px;

    box-shadow:
        0 15px 45px rgba(35, 42, 80, .06);

}


.question-top {

    display: flex;

    justify-content: space-between;

    align-items: center;

}


.question-number {

    color: var(--primary);

    background: #eef0ff;

    border-radius: 999px;

    padding: 6px 11px;

    font-size: 12px;

    font-weight: 850;

}


.difficulty {

    color: var(--muted);

    font-size: 13px;

}


.question-text {

    font-size: 21px;

    font-weight: 650;

    line-height: 1.6;

    margin: 25px 0 18px;

}


.given-data {

    background: #f7f8fc;

    border-radius: 15px;

    padding: 17px;

    display: grid;

    grid-template-columns: repeat(3, 1fr);

    gap: 12px;

    margin-bottom: 25px;

}


.data-item b {

    display: block;

    font-size: 20px;

}


.data-item span {

    color: var(--muted);

    font-size: 12px;

}


.answers {

    display: grid;

    grid-template-columns: repeat(3, 1fr);

    gap: 12px;

}


.answer {

    display: flex;

    flex-direction: column;

    gap: 7px;

}


.answer label {

    color: var(--muted);

    font-size: 12px;

    font-weight: 800;

}


.answer input {

    width: 100%;

    border: 1px solid #d8dce7;

    border-radius: 10px;

    background: white;

    padding: 11px 13px;

    color: var(--text);

    font-size: 18px;

    outline: none;

}


.answer input:focus {

    border-color: var(--primary);

}


.check-button {

    width: 100%;

    margin-top: 22px;

}


/* =========================
   FEEDBACK
========================= */

.feedback {

    margin-top: 16px;

    border-radius: 12px;

    padding: 14px 16px;

    line-height: 1.5;

}


.feedback.correct {

    color: var(--success);

    background: var(--success-bg);

}


.feedback.wrong {

    color: var(--danger);

    background: var(--danger-bg);

}


.hidden {

    display: none !important;

}


/* =========================
   UITLEG BIJ VRAAG
========================= */

.explanation-button {

    width: 100%;

    margin-top: 12px;

    padding: 13px;

    border: 1px solid var(--border);

    border-radius: 12px;

    background: white;

    color: var(--text);

    font-weight: 750;

    cursor: pointer;

    transition: .15s;

}


.explanation-button:hover {

    background: #f7f7ff;

}


.explanation {

    margin-top: 14px;

    padding: 20px;

    background: #f7f8fc;

    border-radius: 15px;

    line-height: 1.65;

}


.explanation h3 {

    font-size: 16px;

    margin-top: 0;

}


.formula-box {

    padding: 15px;

    margin: 12px 0;

    background: #eef0ff;

    border-radius: 12px;

    color: #414568;

    font-weight: 650;

}


/* =========================
   THEORIE
========================= */

.theory {

    margin-top: 25px;

}


.theory-header {

    display: flex;

    align-items: end;

    justify-content: space-between;

    gap: 30px;

    margin-bottom: 15px;

}


.theory-header h2 {

    margin: 12px 0 0;

    font-size: 30px;

}


.theory-header p {

    color: var(--muted);

}


.theory details {

    margin-top: 9px;

    background: white;

    border: 1px solid var(--border);

    border-radius: 15px;

    overflow: hidden;

}


.theory summary {

    display: flex;

    align-items: center;

    gap: 13px;

    padding: 18px 20px;

    list-style: none;

    cursor: pointer;

    font-weight: 750;

}


.theory summary::-webkit-details-marker {

    display: none;

}


.theory-number {

    width: 32px;

    height: 32px;

    display: grid;

    place-items: center;

    flex-shrink: 0;

    border-radius: 9px;

    background: #eef0ff;

    color: var(--primary);

    font-size: 12px;

}


.summary-arrow {

    margin-left: auto;

    font-size: 22px;

    color: var(--muted);

    transition: transform .2s;

}


.theory details[open] .summary-arrow {

    transform: rotate(45deg);

}


.theory-content {

    padding: 0 20px 20px 65px;

    color: #50586c;

    line-height: 1.7;

}


.theory-content h3 {

    color: var(--text);

    font-size: 18px;

}


.theory-content p {

    max-width: 800px;

}


.example-box {

    padding: 15px;

    margin: 14px 0;

    background: #f7f8fc;

    border-left: 4px solid var(--primary);

    border-radius: 10px;

}


.formulas .formula-box {

    margin-bottom: 10px;

}


/* =========================
   RESPONSIVE
========================= */

@media (max-width: 850px) {

    .hero {

        grid-template-columns: 1fr;

        padding-top: 50px;

        gap: 30px;

    }


    .cards {

        grid-template-columns: 1fr;

    }


    .settings-card {

        grid-template-columns: 1fr;

    }


    .practice-header {

        align-items: flex-start;

        flex-direction: column;

    }


    .answers,
    .given-data {

        grid-template-columns: 1fr;

    }


    .theory-header {

        align-items: flex-start;

        flex-direction: column;

        gap: 5px;

    }


    .theory-content {

        padding-left: 20px;

    }

}


@media (max-width: 600px) {

    .navbar {

        padding: 0 4%;

    }


    .nav-links a {

        padding: 8px;

        font-size: 13px;

    }


    .hero {

        padding-left: 5%;

        padding-right: 5%;

    }


    .hero h1 {

        font-size: 44px;

    }


    .mini-formulas {

        grid-template-columns: 1fr;

    }


    .practice-page {

        padding-left: 15px;

        padding-right: 15px;

    }


    .practice-header h1 {

        font-size: 40px;

    }


    .question-card {

        padding: 20px;

    }

}