/* CSS Variables */
:root {
    --color-bg: #f8f9fa;
    --color-surface: #ffffff;
    --color-primary: #2563eb;
    --color-primary-hover: #1d4ed8;
    --color-text: #1f2937;
    --color-text-secondary: #6b7280;
    --color-border: #e5e7eb;
    --color-success: #10b981;
    --color-error: #ef4444;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --transition: 150ms ease;
}

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

/* Base */
html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    min-height: 100vh;
}

/* Container */
.container {
    max-width: 720px;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

/* Header */
.header {
    text-align: center;
    margin-bottom: 3rem;
}

.logo {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 72px;
    height: 72px;
    background: linear-gradient(135deg, var(--color-primary), #7c3aed);
    border-radius: var(--radius-lg);
    color: white;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow-md);
}

.header h1 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 0.5rem;
}

.subtitle {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    max-width: 480px;
    margin: 0 auto;
}

/* Main Form Section */
.main {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 3rem;
}

/* Form */
.form {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.form-group label {
    font-weight: 600;
    font-size: 0.9375rem;
    color: var(--color-text);
}

.form-group textarea {
    width: 100%;
    padding: 0.875rem 1rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    font-family: inherit;
    font-size: 1rem;
    line-height: 1.5;
    resize: vertical;
    transition: border-color var(--transition), box-shadow var(--transition);
    background: var(--color-surface);
}

.form-group textarea:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-group textarea::placeholder {
    color: var(--color-text-secondary);
    opacity: 0.7;
}

.hint {
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
}

/* Checkbox */
.checkbox-label {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    cursor: pointer;
    user-select: none;
    font-weight: 500;
}

.checkbox-label input[type="checkbox"] {
    width: 20px;
    height: 20px;
    cursor: pointer;
    accent-color: var(--color-primary);
}

.checkbox-label span {
    font-weight: 500;
    font-size: 0.9375rem;
}

/* Counter */
.counter {
    display: inline-flex;
    align-items: center;
    gap: 0;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow: hidden;
    width: fit-content;
}

.counter-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 48px;
    height: 48px;
    border: none;
    background: var(--color-surface);
    color: var(--color-text);
    cursor: pointer;
    transition: background-color var(--transition);
}

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

.counter-btn:active {
    background: var(--color-border);
}

.counter input {
    width: 64px;
    height: 48px;
    border: none;
    border-left: 1px solid var(--color-border);
    border-right: 1px solid var(--color-border);
    text-align: center;
    font-family: inherit;
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-text);
    background: var(--color-surface);
    -moz-appearance: textfield;
}

.counter input::-webkit-outer-spin-button,
.counter input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

/* Primary Button */
.btn-primary {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    width: 100%;
    padding: 1rem 1.5rem;
    border: none;
    border-radius: var(--radius-md);
    background: linear-gradient(135deg, var(--color-primary), #4f46e5);
    color: white;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform var(--transition), box-shadow var(--transition), opacity var(--transition);
    box-shadow: var(--shadow-md);
    margin-top: 0.5rem;
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

.btn-primary:active:not(:disabled) {
    transform: translateY(0);
}

.btn-primary:disabled {
    opacity: 0.7;
    cursor: not-allowed;
}

.btn-primary .btn-loading {
    display: none;
}

.btn-primary.loading .btn-text {
    display: none;
}

.btn-primary.loading .btn-loading {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

/* Spinner */
.spinner {
    animation: spin 1s linear infinite;
}

@keyframes spin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

/* Result */
.result {
    margin-top: 1.5rem;
    padding: 1.5rem;
    background: #f0fdf4;
    border: 1px solid #bbf7d0;
    border-radius: var(--radius-md);
    text-align: center;
}

.result-success {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.75rem;
}

.result-success h3 {
    font-size: 1.125rem;
    font-weight: 600;
    color: #166534;
}

.result-success p {
    color: #15803d;
    font-size: 0.9375rem;
}

/* Error */
.error {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-top: 1.5rem;
    padding: 1rem 1.25rem;
    background: #fef2f2;
    border: 1px solid #fecaca;
    border-radius: var(--radius-md);
    color: #dc2626;
    font-size: 0.9375rem;
}

/* Hidden State */
.hidden {
    display: none !important;
}

/* Features Section */
.features {
    margin-bottom: 3rem;
}

.features h2 {
    font-size: 1.25rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 1.5rem;
    color: var(--color-text);
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
}

.feature-card {
    background: var(--color-surface);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--color-border);
    text-align: center;
}

.feature-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 56px;
    height: 56px;
    background: var(--color-bg);
    border-radius: var(--radius-md);
    color: var(--color-primary);
    margin-bottom: 1rem;
}

.feature-card h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--color-text);
}

.feature-card p {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

/* Footer */
.footer {
    text-align: center;
    padding-top: 1.5rem;
    border-top: 1px solid var(--color-border);
}

.footer p {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

/* Responsive */
@media (max-width: 640px) {
    .container {
        padding: 1.5rem 1rem;
    }

    .header h1 {
        font-size: 1.75rem;
    }

    .subtitle {
        font-size: 1rem;
    }

    .main {
        padding: 1.5rem;
    }

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