:root {
    --bg: #f4f7fb;
    --card: #ffffff;
    --primary: #4f46e5;
    --primary-dark: #3730a3;
    --text: #1f2937;
    --muted: #6b7280;
    --border: #e5e7eb;
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    font-family: Arial, Helvetica, sans-serif;
    background: linear-gradient(135deg, #eef2ff 0%, #f8fafc 100%);
    color: var(--text);
    display: grid;
    place-items: center;
}

.container {
    width: min(100%, 480px);
    padding: 24px;
}

.card {
    background: var(--card);
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(79, 70, 229, 0.12);
    padding: 32px 24px;
}

.header {
    text-align: center;
    margin-bottom: 24px;
}

.eyebrow {
    margin: 0 0 8px;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--primary);
    font-size: 12px;
    font-weight: 700;
}

h1 {
    margin: 0;
    font-size: 2rem;
}

.form {
    display: grid;
    gap: 18px;
}

.field-group {
    display: grid;
    gap: 8px;
}

label {
    font-weight: 700;
    font-size: 0.95rem;
}

input {
    width: 100%;
    padding: 14px 16px;
    border: 1px solid var(--border);
    border-radius: 12px;
    font-size: 1rem;
    outline: none;
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

input:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 4px rgba(79, 70, 229, 0.1);
}

button {
    border: none;
    border-radius: 12px;
    background: var(--primary);
    color: white;
    font-weight: 700;
    font-size: 1rem;
    padding: 14px 18px;
    cursor: pointer;
    transition: background 0.2s ease, transform 0.2s ease;
}

button:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
}

.result {
    margin-top: 28px;
    background: #f8fafc;
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 20px 18px;
    text-align: center;
}

.result-label {
    margin: 0;
    color: var(--muted);
    text-transform: uppercase;
    letter-spacing: 0.08em;
    font-size: 0.75rem;
    font-weight: 700;
}

#bmi-value {
    margin: 12px 0 8px;
    font-size: 2.2rem;
    color: var(--primary-dark);
}

#bmi-category {
    margin: 0;
    color: var(--text);
    font-weight: 600;
}