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

:root {
    --color-bg:        #f5f7fa;
    --color-surface:   #ffffff;
    --color-primary:   #3b82f6;
    --color-primary-h: #2563eb;
    --color-border:    #d1d5db;
    --color-text:      #1f2937;
    --color-hint:      #6b7280;
    --color-red:       #ef4444;
    --color-green:     #22c55e;
    --radius:          8px;
    --shadow:          0 4px 16px rgba(0,0,0,.08);
    --transition:      .2s ease;
}

body {
    font-family: system-ui, -apple-system, 'Segoe UI', sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1rem;
}

.container {
    background: var(--color-surface);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 2.5rem 2rem;
    max-width: 480px;
    width: 100%;
}

h1 {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 1.75rem;
    text-align: center;
}

.form-section label {
    display: block;
    font-weight: 600;
    margin-bottom: .5rem;
}

.input-wrapper {
    display: flex;
    gap: .5rem;
}

input[type="text"] {
    flex: 1;
    padding: .6rem .875rem;
    border: 1.5px solid var(--color-border);
    border-radius: var(--radius);
    font-size: 1rem;
    outline: none;
    transition: border-color var(--transition), box-shadow var(--transition);
}

input[type="text"]:focus {
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(59,130,246,.2);
}

button#btn-submit {
    padding: .6rem 1.25rem;
    background: var(--color-primary);
    color: #fff;
    border: none;
    border-radius: var(--radius);
    font-size: .95rem;
    font-weight: 600;
    cursor: pointer;
    transition: background var(--transition), transform var(--transition);
}
button#btn-submit:hover    { background: var(--color-primary-h); }
button#btn-submit:active   { transform: scale(.97); }
button#btn-submit:disabled { opacity: .55; cursor: not-allowed; }

.hint { margin-top: .5rem; font-size: .82rem; color: var(--color-hint); }

kbd {
    background: #e5e7eb;
    border: 1px solid #d1d5db;
    border-radius: 4px;
    padding: 0 .35rem;
    font-size: .8em;
}

#result {
    display: block;
    margin-top: 1.75rem;
    font-size: 1.5rem;
    font-weight: 700;
    min-height: 2rem;
    text-align: center;
    opacity: 0;
    transition: color var(--transition), opacity var(--transition);
}
#result.visible     { opacity: 1; }
#result.color-red   { color: var(--color-red); }
#result.color-green { color: var(--color-green); }
#result.color-error { color: #b91c1c; font-size: 1rem; font-weight: 400; }

.spinner {
    width: 24px; height: 24px;
    border: 3px solid rgba(59,130,246,.3);
    border-top-color: var(--color-primary);
    border-radius: 50%;
    animation: spin .7s linear infinite;
    margin: 0 auto;
}
@keyframes spin { to { transform: rotate(360deg); } }