To make elements of the mainPhoto class stand out, set the height property to 200px.

<html>
<head>
<style>
.mainPhoto {
height:200px;
}

img {
height:100px;
}
</style>
</head>
<body>
<h1>Top Destination</h1>
<img class="mainPhoto" src="https://mimo.app/r/beach.png">
<h2>Other Destinations</h2>
<img src="https://mimo.app/r/market.png">

</html>]]>

Make sure to pick height, followed by 200px.