JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main-container">
        <nav class="navbar navbar-default navbar-fixed-top">
            <div class="container-fluid">
                <div class="btn-group pull-right personal-tools">
                    <a class="btn dropdown-toggle">First header</a>
                </div>
            </div>
        </nav>

    <div>
        <nav class="navbar navbar-default navbar-fixed-top action-bar">
            <div class="container-fluid">
                <ul class="nav nav-pills">
                    <li><a class="project-button"> Second Header</a></li>
                    <li><a>Second Header</a></li>
                </ul>
            </div>
        </nav>
        
        <div class="flex-box">
            <div class="left">
                <ol ui-tree-nodes="" ng-model="root.items">
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list item</li>
                        <li>list...

CSS

html, body {
  height: 100%;
  margin: 0;
}

.header {
    background: lime;
    height: 50px;
}

.flex-box {
    display: flex;
    height: -moz-calc(100% - 50px);
    height: -webkit-calc(100% - 50px);
    height: calc(100% - 50px);
}

.left {
    flex: 1;
    order: 1;
    background: aqua;
    overflow: auto;
}

.right {
    flex: 1;
    order: 2;
    background: yellow;
    overflow:auto;
}

/* Fix for bootstrap box issues in slickgrid */
*,
*:before,
*:after {
  -webkit-box-sizing: content-box;
     -moz-box-sizing: content-box;
          box-sizing: content-box;
}
.container .row *,
.container .row *:before,
.container .row *:after {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
}


/* adding all the other css I have just in case */
body {
    background: none repeat scroll 0 0;
    padding-top: 105px;
}

/* nav-pills custom styling */
.nav > li > a {
    padding: 5px 15px;
}

.nav > li > .separator {
    padding: 5px 15px;
    color: #428bca;
    display: block;
    position: relative;
}

/* Fix for cursor point in angular bootstrap */
.nav, .pagination, .carousel, .panel-title a {
    cursor: pointer;
}

.nav {
    margin-top: 10px;
}

.no-top-margin {
    margin-top: 0px !important;
}

.action-bar {
    top: 50px;
    z-index: 999;
}

#main-container {
    width: 100%;
    display: inline-block;
}

input.editor-text {
    background: none repeat scroll 0 0 transparent;
    border: 0 none;
    height: 100%;
    margin: 0;
    outline: 0 none;
    padding: 0;
    width: 100%;
}

.hide {
    display: none !important;
}

.col-sm-7 {
    padding-left: 0px !important;
    padding-right: 0px !important;
}

.form-signin {
    max-width: 330px;
    padding: 15px;
    margin: 0 auto;
}

.form-signin #userName {
    margin-bottom: -1px;
    border-bottom-right-radius: 0;
    border-bottom-left-radius: 0;
}

.form-signin #userPassword {
    margin-bottom: 10px;
    border-top-left-radius: 0;
   ...