:root {
    --primary-color: #4A90E2; 
    --secondary-color: #F5A623; 
    --success-color: #7ED321; 
    --danger-color: #D0021B; 
    --bg-light: #F7F9FC;
    --bg-white: #FFFFFF;
    --border-color: #E0E6ED;
    --shadow-light: 0 2px 4px rgba(0, 0, 0, 0.05);
    --shadow-heavy: 0 4px 12px rgba(0, 0, 0, 0.1);
    --radius: 8px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: var(--bg-light);
    color: #333;
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    padding: 20px 10px;
}

/* Main app container */
.todo-app {
    width: 100%;
    max-width: 800px;
    background-color: var(--bg-white);
    border-radius: 12px;
    box-shadow: var(--shadow-heavy);
    padding: 30px;
    display: flex;
    flex-direction: column;
    gap: 25px;
}

h1 {
    text-align: center;
    color: var(--primary-color);
    margin-bottom: 10px;
    font-size: 2.5rem;
}

/* Task-addition form */
.todo-form {
    display: grid;
    grid-template-columns: 1fr 150px 100px; /* Text | Date | Button */
    gap: 15px;
    align-items: center;
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 20px;
}

.todo-form__input, .todo-form__date {
    padding: 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 1rem;
    transition: border-color 0.3s;
}

.todo-form__input:focus, .todo-form__date:focus {
    outline: none;
    border-color: var(--primary-color);
}

.todo-form__button {
    padding: 12px;
    background-color: var(--primary-color);
    color: var(--bg-white);
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.3s;
}

.todo-form__button:hover {
    background-color: #3a7bd5;
}

/* Control panel (Filters, Sort, Search) */
.controls-panel {
    display: flex;
    gap: 15px;
    flex-wrap: wrap;
    align-items: center;
    padding-bottom: 15px;
    border-bottom: 1px solid var(--border-color);
}

.controls-panel__search, .controls-panel__filter, .controls-panel__sort {
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 0.95rem;
    flex-grow: 1;
    min-width: 120px;
}

/* Styles for the task list */
.todo-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

/* Styles for a single task */
.todo-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 15px;
    background-color: var(--bg-white);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    transition: background-color 0.3s, box-shadow 0.3s;
    cursor: grab; /* Cursor for Drag-and-Drop */
}

.todo-item[draggable="true"]:hover {
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

/* Drag-and-Drop: Style for the dragged element */
.dragging {
    opacity: 0.4;
    border: 2px dashed var(--primary-color);
    background-color: #E6F3FF;
}

/* Drag-and-Drop: Style for the drop zone */
.drag-over {
    border-top: 2px solid var(--primary-color);
    /* Add a bit of space to show where the element will land */
    padding-top: 20px; 
}


.todo-item__content {
    display: flex;
    align-items: center;
    flex-grow: 1;
    gap: 15px;
}

.todo-item__checkbox {
    /* Hide the default checkbox and apply custom styling */
    position: absolute;
    opacity: 0;
    width: 0;
    height: 0;
}

.todo-item__check-label {
    display: block;
    width: 22px;
    height: 22px;
    border: 2px solid var(--primary-color);
    border-radius: 4px;
    cursor: pointer;
    background-color: var(--bg-white);
    transition: all 0.2s;
    position: relative;
    flex-shrink: 0;
}

.todo-item__checkbox:checked + .todo-item__check-label {
    background-color: var(--success-color);
    border-color: var(--success-color);
}

.todo-item__checkbox:checked + .todo-item__check-label::after {
    content: '✔';
    color: var(--bg-white);
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 14px;
    font-weight: bold;
}

.todo-item__text {
    font-size: 1rem;
    word-break: break-word;
    margin-right: 10px;
}

.todo-item__date {
    font-size: 0.85rem;
    color: #888;
    margin-left: auto; /* Pushes to the date */
    flex-shrink: 0;
}

/* Style for a completed task */
.todo-item--completed {
    background-color: #EAF7E6;
    border-left: 5px solid var(--success-color);
    opacity: 0.8;
}

.todo-item--completed .todo-item__text {
    text-decoration: line-through;
    color: #666;
}

/* Action buttons */
.todo-item__actions {
    display: flex;
    gap: 5px;
    flex-shrink: 0;
}

.action-btn {
    padding: 8px 10px;
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 0.9rem;
    transition: background-color 0.3s;
}

.action-btn--edit {
    background-color: var(--secondary-color);
    color: var(--bg-white);
}

.action-btn--edit:hover {
    background-color: #e59418;
}

.action-btn--delete {
    background-color: var(--danger-color);
    color: var(--bg-white);
}

.action-btn--delete:hover {
    background-color: #b00016;
}

/* Edit mode */
.todo-item__edit-input, .todo-item__edit-date {
    padding: 5px;
    border: 1px solid var(--secondary-color);
    border-radius: 4px;
    font-size: 1rem;
    margin-right: 10px;
}

.todo-item__edit-input {
    flex-grow: 1;
}

/* Responsiveness */
@media (max-width: 650px) {
    .todo-app {
        padding: 20px 15px;
    }
    
    h1 {
        font-size: 2rem;
    }

    .todo-form {
        grid-template-columns: 1fr 1fr; /* Move date to the second row */
        grid-template-rows: auto auto;
        gap: 10px;
    }
    
    .todo-form__input {
        grid-column: 1 / 3; /* Text full width */
    }

    .todo-form__date {
        grid-column: 1 / 2;
    }

    .todo-form__button {
        grid-column: 2 / 3;
    }

    .controls-panel {
        flex-direction: column;
        gap: 10px;
    }
    
    .controls-panel > * {
        width: 100%; /* Controls full width */
        min-width: unset;
    }
    
    .todo-item {
        flex-wrap: wrap;
        gap: 10px;
    }
    
    .todo-item__content {
        order: 1;
        flex-basis: 100%; /* Content full width */
    }
    
    .todo-item__actions {
        order: 3;
        width: 100%;
        justify-content: flex-end;
    }
    
    .todo-item__date {
        order: 2;
        margin-left: 0;
        font-size: 0.9rem;
    }
    
    .todo-item--editing .todo-item__edit-input {
        flex-basis: 100%;
        margin-bottom: 10px;
    }
}