JSFiddle - React, Tailwind, and code Playground

by w3cplus

HTML

<div class="demo">
    <div class="box"></div>
</div>

CSS

.demo {
    width: 300px;
    background: #60f;
    padding: 3px 0;
}
.box {
    background: #f60;
    height: 50px;
    padding:10px;
    border:5px solid green;
    width: 90%;/*写给不支持calc()的浏览器*/
    width:-moz-calc(100% - (10px + 5px) * 2);
    width:-webkit-calc(100% - (10px + 5px) * 2);
    width: calc(100% - (10px + 5px) * 2);
}