JSFiddle - React, Tailwind, and code Playground

HTML

<div id="fixedLeftMenu"></div>
<div id="container">
    <div id="redFixedDiv">
    </div>
    <div id="blueDiv"></div>
</div>

SCSS

#fixedLeftMenu {   
    display:inline-block;height: 50px;background-color:yellow;
    width: 25px;
    position: fixed;    
}

#container {  
    display:inline-block; background-color:orange;
    width: calc(100% - 25px);
    margin-left: 25px;
}

#redFixedDiv {
    height: 100px; background-color: red;  
    width: 25%;
    position: fixed;                       
}
#blueDiv {
    float:right;height: 1000px;background-color: blue;   
    width: calc(100% - 25%);
}