:root {
    --bg-color: #f4f7f6;
    --column-bg: #ebedef;
    --card-bg: #ffffff;
    --text-main: #333;
    --text-muted: #666;
    --accent-color: #4a90e2;
    --border-color: #ddd;
    --shadow: 0 2px 5px rgba(0,0,0,0.1);
    --radius: 8px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
}

.app-container {
    width: 100%;
    max-width: 1200px;
    padding: 2rem;
    box-sizing: border-box;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

h1 {
    font-weight: 700;
    font-size: 1.5rem;
    margin: 0;
}

.header-actions {
    display: flex;
    gap: 10px;
}

#task-input {
    padding: 8px 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    outline: none;
    width: 250px;
}

#add-task-btn {
    padding: 8px 16px;
    background-color: var(--accent-color);
    color: white;
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    font-weight: 600;
    transition: opacity 0.2s;
}

#add-task-btn:hover {
    opacity: 0.9;
}

.kanban-board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    align-items: start;
}

.column {
    background-color: var(--column-bg);
    border-radius: var(--radius);
    padding: 1rem;
    min-height: 500px;
    display: flex;
    flex-direction: column;
    box-shadow: inset 0 0 5px rgba(0,0,0,0.05);
}

.column-header {
    font-weight: 700;
    text-transform: uppercase;
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 1rem;
    text-align: center;
}

.task-list {
    min-height: 450px;
}

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 12px;
    margin-bottom: 10px;
    cursor: grab;
    box-shadow: var(--shadow);
    transition: transform 0.1s, box-shadow 0.1s;
    user-select: none;
}

.card:active {
    cursor: grabbing;
}

.card.dragging {
    opacity: 0.5;
    transform: scale(0.95);
    box-shadow: none;
    border: 2px dashed var(--accent-color);
}