/* Base Styles */
:root {
    --primary-color: #4a6fa5;
    --secondary-color: #166088;
    --accent-color: #4fc3dc;
    --text-color: #333;
    --light-gray: #f5f5f5;
    --medium-gray: #e0e0e0;
    --dark-gray: #888;
    --danger-color: #e74c3c;
    --success-color: #2ecc71;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background-color: white;
    border-radius: 10px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
    overflow: hidden;
}

/* Header Styles */
header {
    background-color: var(--primary-color);
    color: white;
    padding: 20px;
    text-align: center;
}

header h1 {
    margin-bottom: 5px;
    font-weight: 600;
}

header p {
    opacity: 0.8;
    font-size: 0.9rem;
}

/* Form Styles */
.todo-form {
    display: flex;
    padding: 20px;
    border-bottom: 1px solid var(--medium-gray);
}

#task-input {
    flex: 1;
    padding: 12px 15px;
    border: 1px solid var(--medium-gray);
    border-radius: 4px;
    font-size: 1rem;
    outline: none;
    transition: border-color 0.3s;
}

#task-input:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 2px rgba(79, 195, 220, 0.2);
}

#add-task-btn {
    margin-left: 10px;
    padding: 12px 20px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.3s;
}

#add-task-btn:hover {
    background-color: var(--secondary-color);
}

/* Filters Styles */
.filters {
    display: flex;
    padding: 15px 20px;
    background-color: var(--light-gray);
    justify-content: center;
}

.filter-btn {
    margin: 0 5px;
    padding: 8px 15px;
    background-color: transparent;
    border: 1px solid var(--medium-gray);
    border-radius: 20px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: all 0.3s;
}

.filter-btn:hover {
    background-color: var(--medium-gray);
}

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

/* Task List Styles */
#task-list {
    list-style-type: none;
    padding: 0;
    max-height: 400px;
    overflow-y: auto;
}

.task-item {
    display: flex;
    align-items: center;
    padding: 15px 20px;
    border-bottom: 1px solid var(--medium-gray);
    transition: background-color 0.3s;
}

.task-item:hover {
    background-color: var(--light-gray);
}

.task-checkbox {
    margin-right: 15px;
    appearance: none;
    width: 20px;
    height: 20px;
    border: 2px solid var(--dark-gray);
    border-radius: 50%;
    cursor: pointer;
    position: relative;
    transition: all 0.3s;
}

.task-checkbox:checked {
    background-color: var(--success-color);
    border-color: var(--success-color);
}

.task-checkbox:checked::after {
    content: '✓';
    position: absolute;
    color: white;
    font-size: 14px;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.task-text {
    flex: 1;
    font-size: 1rem;
    transition: color 0.3s, text-decoration 0.3s;
}

.completed .task-text {
    color: var(--dark-gray);
    text-decoration: line-through;
}

.delete-btn {
    background-color: transparent;
    border: none;
    color: var(--danger-color);
    cursor: pointer;
    font-size: 1.1rem;
    opacity: 0.7;
    transition: opacity 0.3s;
}

.delete-btn:hover {
    opacity: 1;
}

/* Task Stats Styles */
.task-stats {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 20px;
    background-color: var(--light-gray);
    font-size: 0.9rem;
    color: var(--dark-gray);
}

#clear-completed {
    background-color: transparent;
    border: none;
    color: var(--danger-color);
    cursor: pointer;
    font-size: 0.9rem;
    transition: opacity 0.3s;
}

#clear-completed:hover {
    opacity: 0.8;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 40px 20px;
    color: var(--dark-gray);
}

.empty-state i {
    font-size: 3rem;
    margin-bottom: 15px;
    opacity: 0.3;
}

/* Responsive Styles */
@media (max-width: 600px) {
    .todo-form {
        flex-direction: column;
    }
    
    #add-task-btn {
        margin-left: 0;
        margin-top: 10px;
    }
    
    .filters {
        flex-wrap: wrap;
    }
    
    .filter-btn {
        margin-bottom: 5px;
    }
}

/* Animation */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.task-item {
    animation: fadeIn 0.3s ease-out;
}