:root {
    /* Color Palette - Clean and Professional */
    --primary: #2563eb;
    --primary-dark: #1e40af;
    --secondary: #64748b;
    --success: #10b981;
    --danger: #ef4444;
    --warning: #f59e0b;
    
    --bg-main: #fafafa;
    --bg-card: #ffffff;
    --bg-modal: rgba(0, 0, 0, 0.5);
    
    --text-primary: #0f172a;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    
    --border: #e2e8f0;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    
    --radius: 12px;
    --radius-sm: 8px;
}

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

body {
    font-family: 'Work Sans', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg-main);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Header */
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 30px 0;
    margin-bottom: 30px;
}

.logo {
    font-family: 'Space Mono', monospace;
    font-size: 32px;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.5px;
}

.btn-add {
    background: var(--primary);
    color: white;
    border: none;
    padding: 12px 24px;
    border-radius: var(--radius-sm);
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: var(--shadow-sm);
}

.btn-add:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

/* Main Content */
.main-content {
    animation: fadeIn 0.4s ease;
}

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

/* Project Sections */
.project-section {
    margin-bottom: 40px;
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.project-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
}

.project-title {
    font-size: 20px;
    font-weight: 600;
    color: var(--text-primary);
}

.project-count {
    font-size: 14px;
    color: var(--text-muted);
    background: var(--border);
    padding: 2px 10px;
    border-radius: 12px;
}

/* Task Cards */
.task-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.task-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px;
    display: flex;
    align-items: flex-start;
    gap: 16px;
    transition: all 0.2s ease;
    cursor: pointer;
    position: relative;
    overflow: hidden;
}

.task-card::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 4px;
    background: var(--primary);
    opacity: 0;
    transition: opacity 0.2s ease;
}

.task-card:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
    border-color: var(--primary);
}

.task-card:hover::before {
    opacity: 1;
}

.task-card.completed {
    opacity: 0.6;
}

.task-card.completed .task-title {
    text-decoration: line-through;
}

/* Priority Border */
.task-card.priority-high {
    border-left: 4px solid var(--danger);
}

.task-card.priority-medium {
    border-left: 4px solid var(--warning);
}

.task-card.priority-low {
    border-left: 4px solid var(--secondary);
}

/* Checkbox */
.task-checkbox {
    width: 24px;
    height: 24px;
    border: 2px solid var(--border);
    border-radius: 6px;
    cursor: pointer;
    flex-shrink: 0;
    position: relative;
    transition: all 0.2s ease;
}

.task-checkbox:hover {
    border-color: var(--primary);
}

.task-checkbox.checked {
    background: var(--primary);
    border-color: var(--primary);
}

.task-checkbox.checked::after {
    content: '✓';
    position: absolute;
    color: white;
    font-size: 16px;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

/* Task Content */
.task-content {
    flex: 1;
}

.task-title {
    font-size: 16px;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 4px;
}

.task-meta {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
    margin-top: 8px;
}

.task-due-date,
.task-priority-badge {
    font-size: 13px;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 4px;
}

.task-due-date.overdue {
    color: var(--danger);
    font-weight: 500;
}

.task-due-date.today {
    color: var(--warning);
    font-weight: 500;
}

.task-notes {
    font-size: 14px;
    color: var(--text-secondary);
    margin-top: 8px;
    line-height: 1.5;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-muted);
}

.empty-state-icon {
    font-size: 48px;
    margin-bottom: 16px;
    opacity: 0.5;
}

.empty-state-title {
    font-size: 20px;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--text-secondary);
}

.empty-state-text {
    font-size: 15px;
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--bg-modal);
    z-index: 1000;
    align-items: center;
    justify-content: center;
    animation: modalFadeIn 0.2s ease;
}

.modal.active {
    display: flex;
}

@keyframes modalFadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

.modal-content {
    background: var(--bg-card);
    border-radius: var(--radius);
    width: 90%;
    max-width: 500px;
    max-height: 90vh;
    overflow-y: auto;
    box-shadow: var(--shadow-lg);
    animation: modalSlideIn 0.3s ease;
}

@keyframes modalSlideIn {
    from {
        transform: translateY(-50px);
        opacity: 0;
    }
    to {
        transform: translateY(0);
        opacity: 1;
    }
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 24px 24px 20px;
    border-bottom: 1px solid var(--border);
}

.modal-header h2 {
    font-size: 22px;
    font-weight: 600;
}

.close-btn {
    background: none;
    border: none;
    font-size: 28px;
    color: var(--text-secondary);
    cursor: pointer;
    line-height: 1;
    padding: 0;
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 6px;
    transition: all 0.2s ease;
}

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

/* Form */
#taskForm {
    padding: 24px;
}

.form-group {
    margin-bottom: 20px;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

label {
    display: block;
    font-size: 14px;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 8px;
}

input[type="text"],
input[type="date"],
select,
textarea {
    width: 100%;
    padding: 10px 12px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 15px;
    font-family: inherit;
    color: var(--text-primary);
    transition: all 0.2s ease;
    background: var(--bg-card);
}

input[type="text"]:focus,
input[type="date"]:focus,
select:focus,
textarea:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

textarea {
    resize: vertical;
}

.form-actions {
    display: flex;
    gap: 12px;
    justify-content: flex-end;
    margin-top: 24px;
}

.btn-primary,
.btn-secondary {
    padding: 10px 20px;
    border-radius: var(--radius-sm);
    font-size: 15px;
    font-weight: 500;
    cursor: pointer;
    border: none;
    transition: all 0.2s ease;
}

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

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

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

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

/* Mobile Responsive */
@media (max-width: 768px) {
    .container {
        padding: 16px;
    }

    .header {
        padding: 20px 0;
        margin-bottom: 24px;
    }

    .logo {
        font-size: 24px;
    }

    .btn-add {
        padding: 10px 18px;
        font-size: 14px;
    }

    .project-title {
        font-size: 18px;
    }

    .task-card {
        padding: 16px;
    }

    .form-row {
        grid-template-columns: 1fr;
    }

    .modal-content {
        width: 95%;
        max-height: 95vh;
    }

    .modal-header,
    #taskForm {
        padding: 20px;
    }
}

@media (max-width: 480px) {
    .logo {
        font-size: 20px;
    }

    .btn-add {
        padding: 8px 16px;
        font-size: 13px;
    }

    .task-title {
        font-size: 15px;
    }

    .task-meta {
        font-size: 12px;
    }
}