JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
    <div id="left">
        <div class="ac">
            <div class="a">a</div>
            <div class="c">c</div>
        </div>
        <div id="second" class="ac">
            <div class="a">a</div>
            <div class="c">c</div>
        </div>
    </div>
    <div id="right">
        <div class="b">b</div>
        <div id="hidden"></div>
        <div class="b">b</div>
    </div>
</div>

CSS

#main {
    width: 280px;
    height: auto;
}

#left {
    width: 150px;
    float: left;
    height: auto;
}

#right {
    width: 100px;
    height: auto;
    margin-left: 30px;
    float: left;
}

.ac {
    height: 120px;
}

.a, .c {
    height: 50px;
    background-color: #3F86CE;
}

.c {
    margin-top: 20px;
}

#second { // You also can do this, with pseudo selector :ntn-child;
    margin-top: 150px;    
}

.b {
    height: 150px;
    background-color: #3F86CE;
}

#hidden {
    height: 150px;
    background-color: #fff;
    margin-top: 20px;
    visibility: hidden;
}