JSFiddle - React, Tailwind, and code Playground

HTML

<div class="page">
    <div class="b-container">
        <div class="line">
            <div class="unit size1of3">
                <div class="mod">
                    <div class="b-test-content"></div>
                </div>
            </div>
            <div class="unit size1of3">
                <div class="mod">
                    <div class="b-test-content">
                        <div class="line">
                            <div class="unit size1of3">
                                <div class="mod">
                                    <div class="b-test-content"></div>
                                </div>
                            </div>
                            <div class="unit size1of3">
                                <div class="mod">
                                    <div class="b-test-content"></div>
                                </div>
                            </div>
                            <div class="unit size1of3 lastUnit">
                                <div class="mod">
                                    <div class="b-test-content">10px wider</div>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
            <div class="unit size1of3 lastUnit">
                <div class="mod">
                    <div class="b-test-content"></div>
                </div>
            </div>
        </div>
    </div>
</div>

CSS

@import url("http://www.finn.no/styles/so/core/core.css");
 .b-container {
    border:2px solid green;
}
.b-test-content {
    border: 1px solid red;
    height: 20px;
    font-size: 8px;
}