CSS 상자에 기울어진 모서리를 만드는 방법은 무엇입니까?

<div class="cornered"></div>
<div class="main">Hello</div>

.cornered {
    width: 160px;
    height: 0px;
    border-bottom: 40px solid red;
    border-right: 40px solid white;
}

.main {
    width: 200px;
    height: 200px;
    background-color: red;
}

<div class="outer">
    <div class="cornered">It's possible to put text up here, too...
    </div>
    <div class="main">Hello hello hello hello
    hello hello hello hello hello</div>
</div>

.outer {
    background-color: #ccffff;
    padding: 10px;
    font-size: x-small;
}

.cornered {
    width: 176px;
    height: 0px;
    border-bottom: 40px solid red;
    border-left: 40px solid transparent;
}

.main {
    width: 200px;
    height: 200px;
    background-color: red;
    padding: 0 8px;
}