N'utilisez pas CSS position : absolue pour superposer deux éléments

<div>



<p>You could be tempted to position the header absolute:<br>
</p>

<pre class="brush:php;toolbar:false">.card {
    position: relative;
    width: 300px;
}
.card > * {
    margin: 0;
}
.card header {
    position: absolute;
    width: 100%;
    height: 100%;
    background-color: #fff3;
}

.card {
    display: grid;
    width: 300px;
}
.card > * {
    grid-area: 1/1;
    margin: 0;
}
.card header {
    background-color: #fff3;
}