Consider assigning a class to your images and applying CSS directly to them instead of the surrounding div.
Alternatively
You could utilize background-image in your CSS rather than including the image in your HTML code.
By implementing this CSS, your image will adjust its size based on the container.
.container{
background-color:blue;
width:100%;
height: 300px;
}
.slot-one{
background-color:grey;
height: 50%;
width:50%;
background-size: cover;
background-repeat: no-repeat;
background-position: center;
background-image: url('https://cdn.vox-cdn.com/thumbor/e4KRzS--UsuixA2G8TOCwJ-O024=/1400x1050/filters:format(png)/cdn.vox-cdn.com/uploads/chorus_asset/file/6839749/pokemon.0.png');
}
<div class="container">
<div class="slot-one">
<h1> TEXT</h1>
</div>
</div>