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CSS

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HTML 

              
                <section id="layerswitcher">
  <h1>Base Layers Group</h1>
  <label>Group Visible</label>
  <input id="Group" type="checkbox" />
  
  <h2>Layers</h2>
  <section>
    <label>OSM</label>
    <input id="OSM" type="checkbox"/>
  </section>
  
  <section>
    <label>IGNBaseTodo</label>
    <input id="IGNBaseTodo" type="checkbox" checked/>
   </section>
</section>

<div id="map"></div>
!

CSS 

              
                html, body, #map { width:100%; height:100%; margin:0; }

#layerswitcher {
  width: 240px;
  height: 200px; 
  position: absolute;
  z-index: 10;
  
  background-color: white;
  padding: 5px;
}
!

JS 

              
                  // Create OSM layer
const osm = new ol.layer.Tile({
  source: new ol.source.OSM(),
  visible: false,
 });

// Create IGN Base Todo layer
const baseIGNTodo = new ol.layer.Tile({
    source: new ol.source.XYZ({
    url: 'https://tms-ign-base.ign.es/1.0.0/IGNBaseTodo/{z}/{x}/{-y}.jpeg'
  })
});

// Group layers
const BaseLayerGroup = new ol.layer.Group({});

const collection = new ol.Collection();

// Establecer más capas en el grupo utilizando setLayers
BaseLayerGroup.setLayers(collection);

// Se pueden ir añadiendo y eliminado elementos
// desde un collection
collection.push(osm)
collection.push(baseIGNTodo)

// Create map
const map = new ol.Map({
  layers: [BaseLayerGroup],
  target: 'map',
    view: new ol.View({
    center: ol.proj.fromLonLat([0, 0]),
    zoom: 2
  })
});

// Helper function to get element by selector
const $ = (id) => document.querySelector(id);

// Event listeners for checkboxes
const osmInput = $('#OSM');
osmInput.addEventListener('click', () => osm.setVisible(osmInput.checked));

const baseIGNTodoInput = $('#IGNBaseTodo');
baseIGNTodoInput.addEventListener('click', () => baseIGNTodo.setVisible(baseIGNTodoInput.checked));

const GroupInput = $('#Group');
GroupInput.addEventListener('click', () => {
  const checked = GroupInput.checked;
  BaseLayerGroup.setVisible(GroupInput.checked);
  
  osmInput.checked = checked;
  baseIGNTodoInput.checked = checked;
});
!
999px

Console