:root {
    --bg-color: #f0f2f5;
    --container-bg: #ffffff;
    --text-color: #1c1e21;
    --input-bg: #f5f6f7;
    --border-color: #dddfe2;
    --primary-color: #1877f2;
    --item-bg: #ffffff;
}

body.dark-mode {
    --bg-color: #18191a;
    --container-bg: #242526;
    --text-color: #e4e6eb;
    --input-bg: #3a3b3c;
    --border-color: #3e4042;
    --primary-color: #45bd62;
    --item-bg: #242526;
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    justify-content: center;
    padding: 50px 20px;
    margin: 0;
    transition: all 0.3s ease;
}

.container {
    background: var(--container-bg);
    width: 100%;
    max-width: 450px;
    padding: 25px;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.theme-btn {
    font-size: 1.5rem;
    cursor: pointer;
    border: none;
    background: none;
    transition: transform 0.2s;
}

.theme-btn:hover { transform: scale(1.1); }

.input-group {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
}

input {
    flex: 1;
    padding: 12px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background: var(--input-bg);
    color: var(--text-color);
    outline: none;
}

button#addBtn {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 0 20px;
    border-radius: 8px;
    cursor: pointer;
    font-weight: bold;
}

.filters {
    display: flex;
    gap: 8px;
    margin-bottom: 20px;
}

.filter-btn {
    flex: 1;
    padding: 8px;
    border: 1px solid var(--border-color);
    background: var(--container-bg);
    color: var(--text-color);
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.9rem;
}

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

ul { list-style: none; padding: 0; }

.task-item {
    background: var(--item-bg);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px;
    margin-bottom: 8px;
    border-radius: 8px;
    border: 1px solid var(--border-color);
    transition: 0.2s;
}

.task-item span { cursor: pointer; flex: 1; }

.task-item.completed span {
    text-decoration: line-through;
    color: #8a8d91;
}

.delete-btn {
    color: #f02849;
    background: none;
    border: none;
    cursor: pointer;
    font-weight: bold;
    margin-right: 10px;
}