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

:root {
    --primary: #2563eb;
    --primary-dark: #1e40af;
    --success: #16a34a;
    --error: #dc2626;
    --bg: #0f172a;
    --surface: #1e293b;
    --text: #f1f5f9;
    --text-muted: #94a3b8;
    --border: #334155;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1rem;
}

.container {
    max-width: 500px;
    width: 100%;
}

header {
    text-align: center;
    margin-bottom: 2rem;
}

h1 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-muted);
    font-size: 0.95rem;
}

main {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 2rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.5rem;
    font-size: 0.9rem;
}

.validation-icon {
    display: inline-block;
    width: 20px;
    font-size: 1.1rem;
    margin-left: 0.5rem;
}

.validation-icon.valid::after {
    content: '✓';
    color: var(--success);
}

.validation-icon.invalid::after {
    content: '✗';
    color: var(--error);
}

input {
    width: 100%;
    padding: 0.75rem;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 6px;
    color: var(--text);
    font-size: 1rem;
    font-family: 'Courier New', monospace;
    transition: border-color 0.2s;
}

input:focus {
    outline: none;
    border-color: var(--primary);
}

input::placeholder {
    color: var(--text-muted);
    opacity: 0.5;
}

small {
    display: block;
    color: var(--text-muted);
    font-size: 0.8rem;
    margin-top: 0.25rem;
}

.checkbox-group {
    margin-bottom: 1.5rem;
}

.checkbox-group label {
    display: flex;
    align-items: flex-start;
    gap: 0.5rem;
    font-weight: 400;
    font-size: 0.85rem;
    line-height: 1.5;
    cursor: pointer;
}

.checkbox-group input[type="checkbox"] {
    width: auto;
    margin-top: 0.25rem;
    cursor: pointer;
}

.checkbox-group a {
    color: var(--primary);
    text-decoration: none;
}

.checkbox-group a:hover {
    text-decoration: underline;
}

button {
    width: 100%;
    padding: 0.875rem;
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s;
}

button:hover:not(:disabled) {
    background: var(--primary-dark);
}

button:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.result {
    margin-top: 1.5rem;
    padding: 1rem;
    border-radius: 6px;
    font-size: 0.95rem;
}

.result.hidden {
    display: none;
}

.result.success {
    background: rgba(22, 163, 74, 0.1);
    border: 1px solid var(--success);
    color: var(--success);
}

.result.error {
    background: rgba(220, 38, 38, 0.1);
    border: 1px solid var(--error);
    color: var(--error);
}

.result-title {
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.result-details {
    font-size: 0.85rem;
    opacity: 0.9;
    word-break: break-all;
}

footer {
    text-align: center;
    margin-top: 1.5rem;
    color: var(--text-muted);
    font-size: 0.85rem;
}

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

    main {
        padding: 1.5rem;
    }
}