/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary-color: #64748b;
    --success-color: #10b981;
    --error-color: #ef4444;
    --background: #f8fafc;
    --card-background: #ffffff;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --shadow: 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);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.6;
    padding: 1rem;
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background: var(--background);
    border-radius: 24px;
    box-shadow: var(--shadow-lg);
    overflow: hidden;
}

/* Header */
header {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
    color: white;
    padding: 2rem 1.5rem;
    text-align: center;
}

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

.subtitle {
    font-size: 0.95rem;
    opacity: 0.9;
}

/* Main Content */
main {
    padding: 1.5rem;
}

/* Countdown Card */
.countdown-card {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-light) 100%);
    color: white;
    padding: 2.5rem 1.5rem;
    border-radius: 20px;
    text-align: center;
    margin-bottom: 2rem;
    box-shadow: var(--shadow);
}

.description {
    font-size: 1.1rem;
    font-weight: 500;
    margin-bottom: 1rem;
    opacity: 0.95;
}

.countdown-number {
    font-size: 4.5rem;
    font-weight: 800;
    line-height: 1;
    margin-bottom: 0.5rem;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.countdown-label {
    font-size: 1.3rem;
    font-weight: 500;
    opacity: 0.9;
    margin-bottom: 1rem;
}

.target-date-display {
    font-size: 0.95rem;
    opacity: 0.85;
    font-weight: 400;
}

/* Toggle Section */
.toggle-section {
    margin-bottom: 1.5rem;
    padding: 1rem;
    background: var(--card-background);
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.toggle-container {
    display: flex;
    align-items: center;
    cursor: pointer;
    user-select: none;
}

.toggle-container input[type="checkbox"] {
    display: none;
}

.toggle-slider {
    position: relative;
    width: 52px;
    height: 28px;
    background: var(--border-color);
    border-radius: 14px;
    transition: background 0.3s;
    margin-right: 1rem;
    flex-shrink: 0;
}

.toggle-slider::before {
    content: '';
    position: absolute;
    width: 22px;
    height: 22px;
    background: white;
    border-radius: 50%;
    top: 3px;
    left: 3px;
    transition: transform 0.3s;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.toggle-container input:checked + .toggle-slider {
    background: var(--primary-color);
}

.toggle-container input:checked + .toggle-slider::before {
    transform: translateX(24px);
}

.toggle-label {
    font-weight: 500;
    color: var(--text-primary);
}

/* Date Section */
.date-section {
    background: var(--card-background);
    padding: 1.5rem;
    border-radius: 12px;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

.date-section h2 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 1.25rem;
    color: var(--text-primary);
}

/* Date Inputs */
.date-inputs {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    margin-bottom: 1.25rem;
}

.input-group {
    display: flex;
    flex-direction: column;
}

.input-group label {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

.input-group input {
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.2s, box-shadow 0.2s;
    background: var(--background);
}

.input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.description-group {
    grid-column: 1 / -1;
}

/* Month Grid */
.month-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.75rem;
    margin-bottom: 1rem;
}

.month-btn {
    padding: 0.875rem 0.5rem;
    border: 2px solid var(--border-color);
    background: var(--background);
    border-radius: 8px;
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
    color: var(--text-primary);
}

.month-btn:hover {
    border-color: var(--primary-light);
    background: rgba(99, 102, 241, 0.05);
}

.month-btn.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.month-btn:active {
    transform: scale(0.95);
}

/* Error Message */
.error-message {
    background: #fee2e2;
    color: var(--error-color);
    padding: 1rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    font-weight: 500;
    display: none;
    border-left: 4px solid var(--error-color);
}

.error-message.show {
    display: block;
}

/* Action Buttons */
.action-buttons {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    margin-bottom: 1rem;
}

.btn {
    padding: 1rem;
    border: none;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
    box-shadow: var(--shadow);
}

.btn-primary {
    background: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-secondary {
    background: var(--card-background);
    color: var(--text-secondary);
    border: 2px solid var(--border-color);
}

.btn-secondary:hover {
    border-color: var(--secondary-color);
    color: var(--text-primary);
}

/* Footer */
footer {
    text-align: center;
    padding: 1.5rem;
    color: var(--text-secondary);
    font-size: 0.875rem;
    background: var(--card-background);
    border-top: 1px solid var(--border-color);
}

/* Responsive Design */
@media (max-width: 480px) {
    body {
        padding: 0;
    }

    .container {
        border-radius: 0;
        min-height: 100vh;
    }

    header h1 {
        font-size: 1.75rem;
    }

    .countdown-number {
        font-size: 3.5rem;
    }

    .month-grid {
        grid-template-columns: repeat(3, 1fr);
    }

    .action-buttons {
        grid-template-columns: 1fr;
    }
}

@media (min-width: 768px) {
    body {
        padding: 2rem;
    }

    main {
        padding: 2rem;
    }

    .countdown-card {
        padding: 3rem 2rem;
    }

    .countdown-number {
        font-size: 5.5rem;
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.countdown-card {
    animation: fadeIn 0.5s ease-out;
}

/* Accessibility */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}