<body >
<div class="parent">
<div class="child"><p>dddsdfsdabcdd</p></div>
</div>
<body>
body {
width: 100vw;
height: 100vh;
}
.parent {
position: relative;
width: 200px;
background: red;
}
.child {
width: 100%;
position: absolute;
background: yellow;
}
.parent::before {
width: 100%;
position: absolute;
content: '';
background: green;
padding-top: 100%;
}