:root {
    color-scheme: light;
    font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    background: #f4f6fb;
    color: #202a44;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    display: grid;
    place-items: center;
    padding: 24px;
    background: linear-gradient(180deg, #edf2fb 0%, #f9fbff 100%);
}

.page-shell {
    width: min(960px, 100%);
}

.card {
    background: #ffffff;
    border: 1px solid rgba(32, 42, 68, 0.08);
    border-radius: 24px;
    box-shadow: 0 28px 70px rgba(47, 59, 93, 0.12);
    padding: 32px;
}

.panel-header {
    display: grid;
    gap: 18px;
    margin-bottom: 28px;
}

.eyebrow {
    margin: 0;
    color: #596b97;
    font-size: 0.85rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
}

h1 {
    margin: 0;
    font-size: clamp(2rem, 2.4vw, 2.6rem);
    line-height: 1.05;
}

.panel-description {
    margin: 0;
    max-width: 68ch;
    color: #546183;
    line-height: 1.85;
}

.merge-form {
    display: grid;
    gap: 20px;
}

.form-group {
    display: grid;
    gap: 10px;
}

label {
    font-weight: 600;
    color: #27325c;
}

input[type="file"] {
    padding: 14px 12px;
    border-radius: 16px;
    border: 1px solid rgba(32, 42, 68, 0.18);
    background: #f8fafc;
    color: #1b243a;
}

.hint {
    margin: 0;
    color: #5f6d94;
    font-size: 0.95rem;
}

.file-options {
    display: grid;
    gap: 16px;
}

.file-card {
    border: 1px solid rgba(32, 42, 68, 0.1);
    border-radius: 18px;
    background: #f8fbff;
    padding: 18px;
}

.file-card h2 {
    margin: 0 0 12px;
    font-size: 1rem;
    color: #1f2b4f;
}

.row-range {
    display: grid;
    gap: 10px;
    grid-template-columns: repeat(2, minmax(140px, 1fr));
}

.row-range label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
}

.row-range input {
    width: 100%;
    padding: 12px 14px;
    border-radius: 14px;
    border: 1px solid rgba(32, 42, 68, 0.14);
    background: white;
    color: #1a243f;
}

.form-actions {
    display: flex;
    justify-content: flex-end;
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    border: none;
    border-radius: 16px;
    padding: 14px 26px;
    font-size: 1rem;
    font-weight: 700;
    cursor: pointer;
    transition: transform 0.18s ease, box-shadow 0.18s ease, background-color 0.18s ease;
}

.btn-primary {
    background: linear-gradient(135deg, #3a74ff, #1f5bff);
    color: white;
    box-shadow: 0 16px 30px rgba(58, 116, 255, 0.18);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 20px 34px rgba(58, 116, 255, 0.24);
}

@media (max-width: 640px) {
    body {
        padding: 16px;
    }

    .card {
        padding: 24px;
    }

    .form-actions {
        justify-content: stretch;
    }

    .btn {
        width: 100%;
    }
}