<!DOCTYPE html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
<title>border-box and fit-content should include borders</title>
<style>
    .wrapper {
        border: 1px solid red;
        width: 540px;
    }
    .item {
        background-color: blue;
        padding: 10px 20px;
    }
    .content {
        width: 500px;
        height: 50px;
        background-color: green;
    }
</style>
<div class="wrapper"><div class="item"><div class="content"></div></div></div>
