:root {
    --color-primary: #4a90d9;
    --color-primary-hover: #357abd;
    --color-text: #333;
    --color-muted: #888;
    --color-border: #ddd;
    --color-bg: #f8f9fa;
    --color-surface: #fff;
    --color-error: #d32f2f;
    --radius: 6px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
        Helvetica, Arial, sans-serif;
    line-height: 1.6;
    color: var(--color-text);
    background: var(--color-bg);
    padding: 1rem;
}

.container {
    max-width: 600px;
    margin: 2rem auto;
    background: var(--color-surface);
    border-radius: 10px;
    padding: 2rem;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
}

h1 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    text-align: center;
    font-weight: 700;
    letter-spacing: -0.02em;
}

/* Add form */

.add-form {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1.25rem;
}

.add-form input[type="text"] {
    flex: 1;
    padding: 0.55rem 0.75rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    font-size: 0.95rem;
    transition: border-color 0.15s, box-shadow 0.15s;
}

.add-form input[type="text"]:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.15);
}

.add-form button {
    padding: 0.55rem 1.25rem;
    background: var(--color-primary);
    color: #fff;
    border: none;
    border-radius: var(--radius);
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.15s;
    white-space: nowrap;
}

.add-form button:hover {
    background: var(--color-primary-hover);
}

/* Filters */

.filters {
    display: flex;
    gap: 0.4rem;
    margin-bottom: 1rem;
}

.filter-btn {
    padding: 0.35rem 0.9rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-surface);
    font-size: 0.85rem;
    cursor: pointer;
    color: #666;
    transition: all 0.15s;
}

.filter-btn:hover {
    background: #f0f0f0;
}

.filter-btn.active {
    background: var(--color-primary);
    color: #fff;
    border-color: var(--color-primary);
    font-weight: 600;
}

/* Task list items */

.task-item {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.65rem 0;
    border-bottom: 1px solid #eee;
}

.task-item:last-child {
    border-bottom: none;
}

.task-item input[type="checkbox"] {
    width: 1.15rem;
    height: 1.15rem;
    cursor: pointer;
    flex-shrink: 0;
    accent-color: var(--color-primary);
}

.task-title {
    flex: 1;
    word-break: break-word;
}

.task-title.done {
    text-decoration: line-through;
    opacity: 0.45;
    color: var(--color-muted);
}

.task-item button {
    padding: 0.25rem 0.6rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-surface);
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.15s;
    white-space: nowrap;
}

.task-item button:hover {
    background: #f0f0f0;
}

.btn-delete:hover {
    background: #fef0f0;
    border-color: var(--color-error);
    color: var(--color-error);
}

/* Empty state */

.empty-state {
    text-align: center;
    color: #aaa;
    padding: 2.5rem 1rem;
    font-style: italic;
}

/* Edit form */

.task-item.editing {
    background: #f0f7ff;
    border-radius: var(--radius);
    padding: 0.65rem 0.75rem;
    flex-wrap: wrap;
}

.edit-form {
    display: flex;
    gap: 0.5rem;
    flex: 1;
    align-items: center;
}

.edit-form input[type="text"] {
    flex: 1;
    padding: 0.4rem 0.6rem;
    border: 1px solid var(--color-primary);
    border-radius: var(--radius);
    font-size: 0.95rem;
    transition: box-shadow 0.15s;
}

.edit-form input[type="text"]:focus {
    outline: none;
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.15);
}

/* Error message */

.error-message {
    color: var(--color-error);
    font-size: 0.85rem;
    padding: 0.4rem 0;
    margin-bottom: 0.25rem;
    width: 100%;
}

/* Mobile responsive */

@media (max-width: 480px) {
    body {
        padding: 0.5rem;
    }

    .container {
        margin: 0.5rem auto;
        padding: 1.25rem;
        border-radius: 8px;
    }

    h1 {
        font-size: 1.3rem;
        margin-bottom: 1rem;
    }

    .task-item {
        gap: 0.5rem;
        padding: 0.5rem 0;
    }

    .task-item button {
        padding: 0.2rem 0.4rem;
        font-size: 0.75rem;
    }

    .edit-form {
        flex-wrap: wrap;
    }

    .edit-form input[type="text"] {
        min-width: 0;
    }
}