/* ===== CSS Variables ===== */
:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --border-color: #30363d;
    --text-primary: #f0f6fc;
    --text-secondary: #8b949e;
    --accent-blue: #58a6ff;
    --accent-green: #3fb950;
    --accent-yellow: #d29922;
    --accent-red: #f85149;
    --accent-purple: #a371f7;
    --shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
    --radius: 8px;
    --transition: all 0.2s ease;
}

/* ===== Reset & Base ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans TC', Helvetica, Arial, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== Header ===== */
header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1600px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

header h1 {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
}

.header-actions {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
}

/* ===== Buttons ===== */
.btn-primary, .btn-secondary, .btn-danger {
    padding: 0.5rem 1rem;
    border: none;
    border-radius: var(--radius);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

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

.btn-primary:hover {
    background: #79b8ff;
    transform: translateY(-1px);
}

.btn-secondary {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

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

.btn-danger {
    background: var(--accent-red);
    color: white;
}

.btn-danger:hover {
    background: #ff7b72;
}

/* ===== Main Board ===== */
main {
    flex: 1;
    padding: 1.5rem;
    overflow-x: auto;
}

.board {
    display: grid;
    grid-template-columns: repeat(4, minmax(280px, 1fr));
    gap: 1rem;
    max-width: 1600px;
    margin: 0 auto;
    min-height: calc(100vh - 200px);
}

/* ===== Columns ===== */
.column {
    background: var(--bg-secondary);
    border-radius: var(--radius);
    border: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    max-height: calc(100vh - 180px);
}

.column-header {
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: sticky;
    top: 0;
    background: var(--bg-secondary);
    border-radius: var(--radius) var(--radius) 0 0;
}

.column-header h2 {
    font-size: 1rem;
    font-weight: 600;
}

.task-count {
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    padding: 0.25rem 0.5rem;
    border-radius: 12px;
    font-size: 0.75rem;
    font-weight: 600;
}

.task-list {
    flex: 1;
    padding: 0.75rem;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

/* Column specific colors */
.column[data-status="todo"] .column-header h2 { color: var(--accent-blue); }
.column[data-status="in-progress"] .column-header h2 { color: var(--accent-yellow); }
.column[data-status="done"] .column-header h2 { color: var(--accent-green); }
.column[data-status="on-hold"] .column-header h2 { color: var(--accent-purple); }

/* ===== Task Cards ===== */
.task-card {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 0.75rem;
    cursor: grab;
    transition: var(--transition);
    position: relative;
}

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

.task-card.dragging {
    opacity: 0.5;
    cursor: grabbing;
}

.task-card.drag-over {
    border-color: var(--accent-green);
    background: rgba(63, 185, 80, 0.1);
}

.task-card-header {
    display: flex;
    align-items: flex-start;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.priority-indicator {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    flex-shrink: 0;
    margin-top: 6px;
}

.priority-low { background: var(--accent-green); }
.priority-medium { background: var(--accent-yellow); }
.priority-high { background: var(--accent-red); }

.task-title {
    font-size: 0.875rem;
    font-weight: 500;
    line-height: 1.4;
    flex: 1;
}

.task-description {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.task-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 0.25rem;
    margin-bottom: 0.5rem;
}

.tag {
    font-size: 0.65rem;
    padding: 0.15rem 0.4rem;
    border-radius: 4px;
    background: rgba(88, 166, 255, 0.2);
    color: var(--accent-blue);
}

.task-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.7rem;
    color: var(--text-secondary);
}

/* ===== Modal ===== */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
    z-index: 1000;
    align-items: center;
    justify-content: center;
    padding: 1rem;
}

.modal.active {
    display: flex;
}

.modal-content {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    width: 100%;
    max-width: 480px;
    max-height: 90vh;
    overflow-y: auto;
    animation: slideIn 0.2s ease;
}

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

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

.modal-header h3 {
    font-size: 1.125rem;
    font-weight: 600;
}

.close-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 1.5rem;
    cursor: pointer;
    padding: 0;
    line-height: 1;
}

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

/* ===== Form ===== */
form {
    padding: 1rem;
}

.form-group {
    margin-bottom: 1rem;
}

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

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

input, textarea, select {
    width: 100%;
    padding: 0.5rem 0.75rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    color: var(--text-primary);
    font-size: 0.875rem;
    font-family: inherit;
    transition: var(--transition);
}

input:focus, textarea:focus, select:focus {
    outline: none;
    border-color: var(--accent-blue);
    box-shadow: 0 0 0 2px rgba(88, 166, 255, 0.2);
}

textarea {
    resize: vertical;
    min-height: 80px;
}

.form-actions {
    display: flex;
    justify-content: flex-end;
    gap: 0.5rem;
    padding: 1rem;
    border-top: 1px solid var(--border-color);
}

/* ===== Detail Modal ===== */
#detailContent {
    padding: 1rem;
}

#detailContent .detail-row {
    margin-bottom: 1rem;
}

#detailContent .detail-label {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

#detailContent .detail-value {
    font-size: 0.9rem;
}

/* ===== Footer ===== */
footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: 0.75rem 2rem;
    text-align: center;
    font-size: 0.75rem;
    color: var(--text-secondary);
}

/* ===== Scrollbar ===== */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-secondary);
}

/* ===== Drop Zone Indicator ===== */
.task-list.drag-over {
    background: rgba(88, 166, 255, 0.05);
    border: 2px dashed var(--accent-blue);
    border-radius: var(--radius);
}

/* ===== Empty State ===== */
.empty-state {
    text-align: center;
    padding: 2rem 1rem;
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* ===== Responsive ===== */
@media (max-width: 1200px) {
    .board {
        grid-template-columns: repeat(2, minmax(280px, 1fr));
    }
}

@media (max-width: 768px) {
    .board {
        grid-template-columns: 1fr;
    }
    
    .header-content {
        flex-direction: column;
        align-items: stretch;
    }
    
    .header-actions {
        justify-content: center;
    }
    
    .column {
        max-height: none;
    }
}