JSFiddle - React, Tailwind, and code Playground

HTML

<div class="layout">
  <div class="header z-depth-2">
    <div class="dropdown-toogle">
      <div class="dropdown-menu">
      </div>
    </div>
  </div>
  <div class="page-wrapper">
    <div class="sidebar z-depth-2">
    </div>
    <div class="content">
    </div>
  </div>
</div>

CSS

.layout {
  width: 100%;
  height: 100%;
  position: relative;
}

.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 70px;
  background-color: blue;
  z-index: 101;
}

.sidebar {
  position: fixed;
  top: 70px;
  left: 0;
  width: 200px;
  background-color: green;
  bottom: 0;
  z-index:101;
}

.content {
  padding-left: 200px;
  width: 100%;
  height: 100%;
}

.page-wrapper {
  padding-top: 70px;
  height: 100%;
}

.dropdown-toogle {
  margin-right: 100px;
  float: right;
  position: relative;
  height: 100%;
  width: 50px;
  background-color: yellow;
}

.dropdown-menu {
  position: absolute;
  top: 100%;
  right: 0;
  width: 400px;
  height: 200px;
  background-color: grey;
  z-index:1000;
}

.z-depth-2 {
    box-shadow: 0 4px 5px 0 rgba(0, 0, 0, 0.14), 0 1px 10px 0 rgba(0, 0, 0, 0.12), 0 2px 4px -1px rgba(0, 0, 0, 0.3);
}