Edit in JSFiddle

// resize map
const mapdiv = document.getElementById('mapid');
var margin;
if (document.all) {
  margin = parseInt(document.body.currentStyle.marginTop, 10) + parseInt(document.body.currentStyle.marginBottom, 10);
} else {
  margin = parseInt(document.defaultView.getComputedStyle(document.body, '').getPropertyValue('margin-top')) + parseInt(document.defaultView.getComputedStyle(document.body, '').getPropertyValue('margin-bottom'));
}
mapdiv.style.height = (window.innerHeight - margin) + 'px';

/////
var map = L.map('mapid').setView([22.29227, 114.20847], 16);

var apikey = 'f4d3e21d4fc14954a1d5930d4dde3809'
var apikey = '584b2fa686f14ba283874318b3b8d6b0' //api.hkmapservice.gov.hk starter key
L.tileLayer('https://api.hkmapservice.gov.hk/osm/xyz/basemap/WGS84/tile/{z}/{x}/{y}.png?key=' + apikey, {
  attribution: "<a href='https://api.portal.hkmapservice.gov.hk/disclaimer' target='_blank'>&copy; Map from Lands Department <img src='https://api.hkmapservice.gov.hk/mapapi/landsdlogo.jpg' style='width:25px;height:25px'/></a>",
  maxZoom: 19,
  id: 'APIKEY'
}).addTo(map);


L.tileLayer('https://api.hkmapservice.gov.hk/osm/xyz/label-tc/WGS84/tile/{z}/{x}/{y}.png?key=' + apikey, {
  //attribution: "<a href='https://api.portal.hkmapservice.gov.hk/disclaimer' target='_blank'>&copy;Map from Lands Department</a>",
  maxZoom: 19,
  id: 'APIKEY'
}).addTo(map);

#mapid {
  height: 530px;
}

.leaflet-container .leaflet-control-attribution {
  background: transparent;
}

<div id="mapid"></div>