:root {
    --primary-color: #4f46e5;
    --primary-hover: #4338ca;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-color: #1e293b;
    --border-color: #e2e8f0;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.5;
    padding: 2rem;
}

.container {
    max-width: 850px;
    margin: 0 auto;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

h1 {
    font-size: 1.875rem;
    font-weight: 700;
    color: var(--text-color);
}

.controls {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

.input-group {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.input-group label {
    font-size: 0.875rem;
    font-weight: 600;
}

.input-group input,
.input-group select {
    padding: 0.4rem;
    border: 1px solid var(--border-color);
    border-radius: 0.375rem;
    font-size: 0.875rem;
}

.input-group input {
    width: 60px;
}

button {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
    font-weight: 600;
    border-radius: 0.375rem;
    cursor: pointer;
    transition: all 0.2s;
    border: 1px solid transparent;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background-color: var(--primary-hover);
}

.btn-secondary {
    background-color: white;
    border-color: var(--border-color);
    color: var(--text-color);
}

.btn-secondary:hover {
    background-color: var(--bg-color);
}

.worksheet {
    background-color: var(--card-bg);
    padding: 3rem;
    border-radius: 0.5rem;
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
}

.worksheet-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    border-bottom: 2px solid var(--text-color);
    padding-bottom: 1rem;
    margin-bottom: 2rem;
}

.header-text {
    flex-grow: 1;
}

.header-text h2 {
    margin-bottom: 1em;
}

.qr-code {
    width: 25mm;
    height: 25mm;
    margin-left: 2rem;
}

.student-info {
    display: flex;
    gap: 2rem;
}

.info-item {
    border-bottom: 1px solid #000;
    min-width: 200px;
}

.problems-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 3rem 2rem;
}

.problem {
    display: flex;
    flex-direction: column;
    font-size: 1.25rem;
}

.problem-number {
    font-size: 0.875rem;
    font-weight: bold;
    margin-bottom: 0.5rem;
}

.division-box {
    display: flex;
    align-items: flex-end;
    margin-left: 1rem;
}

.divisor {
    padding-right: 0.5rem;
}

.dividend {
    border-left: 2px solid #000;
    border-top: 2px solid #000;
    padding: 0.25rem 0.5rem;
    min-width: 80px;
}

@media screen and (max-width: 768px) {
    body {
        padding: 1rem;
    }

    header {
        flex-direction: column;
        gap: 1.5rem;
        text-align: center;
    }

    .controls {
        flex-wrap: wrap;
        justify-content: center;
        gap: 1rem;
    }

    .input-group {
        width: auto;
    }

    .worksheet {
        padding: 1.5rem;
    }

    .worksheet-header {
        flex-direction: column;
        align-items: center;
        text-align: left;
        gap: 1.5rem;
    }

    .student-info {
        flex-direction: column;
        gap: 1rem;
        align-items: flex-start;
    }

    .info-item {
        min-width: 100%;
    }

    .qr-code {
        margin-left: 0;
    }

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

@media screen and (max-width: 600px) {
    h1 {
        font-size: 1.5rem;
    }

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

    .controls button {
        width: 100%;
    }
}

@media print {
    @page {
        margin: 0.5in;
    }

    body {
        padding: 0;
        margin: 0;
        background-color: white;
    }

    .controls,
    header {
        display: none !important;
    }

    .worksheet {
        box-shadow: none;
        padding: 0;
        margin: 0;
        page-break-after: always;
    }

    .worksheet:last-child {
        page-break-after: auto;
    }

    .worksheet-header {
        margin-bottom: 1.5rem;
    }

    .problems-grid {
        gap: 2rem 1.5rem;
    }

    .container {
        max-width: 100%;
        margin: 0;
        padding: 0;
    }
}

/* Hub Styles */
.hub-header {
    text-align: center;
    margin-bottom: 4rem;
    animation: fadeInDown 0.8s ease-out;
}

.hub-header h1 {
    font-size: 3rem;
    margin-bottom: 1rem;
    background: linear-gradient(135deg, var(--primary-color), #8b5cf6);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hub-header p {
    font-size: 1.25rem;
    color: #64748b;
}

.grid-hub {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    padding-bottom: 4rem;
}

.card {
    background: var(--card-bg);
    border-radius: 1rem;
    padding: 2rem;
    box-shadow: var(--shadow);
    text-decoration: none;
    color: inherit;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    border: 1px solid var(--border-color);
    position: relative;
    overflow: hidden;
}

.card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: var(--primary-color);
    transform: scaleX(0);
    transition: transform 0.3s ease;
}

.card:hover {
    transform: translateY(-8px);
    box-shadow: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
    border-color: var(--primary-color);
}

.card:hover::before {
    transform: scaleX(1);
}

.card-icon {
    font-size: 3rem;
    margin-bottom: 1.5rem;
    background: #f1f5f9;
    width: 80px;
    height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    transition: transform 0.3s ease;
}

.card:hover .card-icon {
    transform: rotate(5deg) scale(1.1);
}

.card h3 {
    font-size: 1.5rem;
    margin-bottom: 0.75rem;
}

.card p {
    color: #64748b;
    font-size: 0.95rem;
}

.card.disabled {
    opacity: 0.7;
    cursor: default;
    pointer-events: none;
}

.card.disabled .badge {
    background: #e2e8f0;
    color: #64748b;
}

.badge {
    background: #e0e7ff;
    color: var(--primary-color);
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: 0.75rem;
    font-weight: 700;
    margin-top: 1rem;
    text-transform: uppercase;
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}