body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f0f2f5;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

.container {
    background: #ffffff;
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 550px;
    box-sizing: border-box;
}

h1 {
    text-align: center;
    color: #333;
    margin-bottom: 30px;
    font-weight: 600;
}

.input-group {
    display: flex;
    margin-bottom: 25px;
}

#new-todo {
    flex-grow: 1;
    padding: 12px 15px;
    border: 1px solid #ddd;
    border-radius: 8px 0 0 8px;
    font-size: 16px;
    outline: none;
    transition: border-color 0.2s;
}

#new-todo:focus {
    border-color: #1877f2;
    box-shadow: 0 0 0 3px rgba(24, 119, 242, 0.2);
}

#add-button {
    padding: 12px 20px;
    background-color: #1877f2;
    color: white;
    border: none;
    cursor: pointer;
    border-radius: 0 8px 8px 0;
    font-size: 16px;
    font-weight: 500;
    transition: background-color 0.2s;
}

#add-button:hover {
    background-color: #166fe5;
}

.controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    padding: 0 5px;
}

.filter-buttons button {
    background: none;
    border: 1px solid #ddd;
    padding: 8px 15px;
    margin-right: 8px;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.2s, color 0.2s;
}

.filter-buttons button:hover {
    background-color: #eee;
}

.filter-buttons button.active {
    background-color: #1877f2;
    color: white;
    border-color: #1877f2;
}

#clear-completed {
    background-color: #dc3545;
    color: white;
    border: none;
    padding: 8px 15px;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.2s;
}

#clear-completed:hover {
    background-color: #c82333;
}

#todo-list {
    list-style: none;
    padding: 0;
}

#todo-list li {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: #f8f9fa;
    padding: 15px;
    margin-bottom: 12px;
    border-radius: 8px;
    border-left: 5px solid #1877f2;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.05);
    transition: all 0.2s;
}

#todo-list li.completed {
    background: #e9ecef;
    border-left: 5px solid #28a745;
    opacity: 0.7;
}

.todo-content {
    display: flex;
    align-items: center;
    flex-grow: 1;
}

.todo-text {
    margin-left: 10px;
    cursor: pointer;
    flex-grow: 1;
    word-break: break-word;
}

#todo-list li.completed .todo-text {
    text-decoration: line-through;
    color: #6c757d;
}

.todo-actions {
    display: flex;
    gap: 8px;
}

.action-button {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 14px;
    padding: 5px;
    border-radius: 4px;
    transition: background-color 0.2s;
}

.edit-button {
    color: #ffc107;
}

.edit-button:hover {
    background-color: #fff3cd;
}

.delete-button {
    color: #dc3545;
}

.delete-button:hover {
    background-color: #f8d7da;
}

.checkbox-label {
    display: block;
    position: relative;
    cursor: pointer;
    padding-left: 25px;
}

.checkbox-label input {
    position: absolute;
    opacity: 0;
    cursor: pointer;
    height: 0;
    width: 0;
}

.checkmark {
    position: absolute;
    top: 0;
    left: 0;
    height: 20px;
    width: 20px;
    background-color: #eee;
    border-radius: 4px;
    transition: background-color 0.2s;
}

.checkbox-label:hover input ~ .checkmark {
    background-color: #ccc;
}

.checkbox-label input:checked ~ .checkmark {
    background-color: #28a745;
}

.checkmark:after {
    content: "";
    position: absolute;
    display: none;
}

.checkbox-label input:checked ~ .checkmark:after {
    display: block;
}

.checkbox-label .checkmark:after {
    left: 7px;
    top: 3px;
    width: 5px;
    height: 10px;
    border: solid white;
    border-width: 0 3px 3px 0;
    transform: rotate(45deg);
}

.license-footer {
    margin-top: 30px;
    font-size: 12px;
    color: #6c757d;
}

.license-footer a {
    color: #1877f2;
    text-decoration: none;
}

.data-management {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-bottom: 20px;
    padding-top: 10px;
    border-top: 1px solid #eee;
}

.data-management button {
    padding: 8px 15px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 14px;
    transition: background-color 0.2s;
}

#export-data {
    background-color: #007bff;
    color: white;
}

#export-data:hover {
    background-color: #0056b3;
}

#import-data {
    background-color: #28a745;
    color: white;
}

#import-data:hover {
    background-color: #1e7e34;
}