:root {
    --bg: #f8f9fa;
    --text: #212529;
    --card: #ffffff;
    --accent: #007bff;
    --accent-hover: #0056b3;
    --border: #dee2e6;
}

[data-theme="dark"] {
    --bg: #121212;
    --text: #e0e0e0;
    --card: #1e1e1e;
    --accent: #0d6efd;
    --accent-hover: #0b5ed7;
    --border: #343a40;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
    padding: 2rem 1rem;
    transition: background 0.3s;
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background: var(--card);
    border-radius: 12px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    overflow: hidden;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem 2rem;
    border-bottom: 1px solid var(--border);
}

h1 {
    font-size: 1.8rem;
    font-weight: 600;
}

#theme-toggle {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 50%;
    transition: transform 0.2s;
}

#theme-toggle:hover {
    transform: rotate(30deg);
}

.input-area {
    padding: 1.5rem 2rem;
    display: flex;
    gap: 0.75rem;
    background: var(--card);
}

#task-input {
    flex: 1;
    padding: 0.85rem 1rem;
    border: 2px solid var(--border);
    border-radius: 8px;
    font-size: 1.05rem;
    outline: none;
    transition: border 0.2s;
}

#task-input:focus {
    border-color: var(--accent);
}

#add-btn {
    padding: 0 1.5rem;
    background: var(--accent);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    cursor: pointer;
    font-weight: 600;
}

#add-btn:hover {
    background: var(--accent-hover);
}

.filters {
    display: flex;
    padding: 0 2rem;
    border-bottom: 1px solid var(--border);
}

.filters button {
    flex: 1;
    padding: 0.85rem;
    background: none;
    border: none;
    font-size: 1rem;
    cursor: pointer;
    color: var(--text);
    border-bottom: 3px solid transparent;
    transition: all 0.2s;
}

.filters button.active {
    border-bottom-color: var(--accent);
    font-weight: 600;
    color: var(--accent);
}

.task-list {
    min-height: 300px;
    list-style: none;
    padding: 0.5rem 0;
}

.task-item {
    display: flex;
    align-items: center;
    padding: 1rem 2rem;
    border-bottom: 1px solid var(--border);
    transition: background 0.2s;
}

.task-item:hover {
    background: rgba(0, 123, 255, 0.05);
}

.task-item.completed {
    opacity: 0.75;
}

.task-item input[type="checkbox"] {
    margin-right: 1rem;
    transform: scale(1.3);
    accent-color: var(--accent);
}

.task-text {
    flex: 1;
    font-size: 1.1rem;
    word-break: break-word;
}

.task-text.completed {
    text-decoration: line-through;
    color: #6c757d;
}

.delete-btn {
    background: none;
    border: none;
    font-size: 1.4rem;
    color: #dc3545;
    cursor: pointer;
    padding: 0.25rem 0.5rem;
    border-radius: 4px;
    opacity: 0.7;
}

.delete-btn:hover {
    opacity: 1;
    background: rgba(220, 53, 69, 0.1);
}

.footer {
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.95rem;
    color: #6c757d;
    border-top: 1px solid var(--border);
}

@media (max-width: 500px) {
    .container {
        margin: 0;
        border-radius: 0;
    }
}