JSFiddle - React, Tailwind, and code Playground

HTML

<div class="modal">
      <div class="modal-title">
        Header
      </div>
      <div class="modal-content">
        <div class="button-group">
          <div class="button selected">Button One</div>
          <div class="button">Button Two</div>
        </div>
        <div class="list"></div>
          <div class="item">Item 1</div>
          <div class="item">Item 2</div>
          <div class="item">Item 3</div>
          <div class="item">Item 4</div>
          <div class="item">Item 5</div>
          <div class="item">Item 6</div>
          <div class="item">Item 7</div>
          <div class="item">Item 8</div>
          <div class="item">Item 9</div>
          <div class="item">Item 10</div>
          <div class="item">Item 11</div>
          <div class="item">Item 12</div>
          <div class="item">Item 13</div>
          <div class="item">Item 14</div>
          <div class="item">Item 15</div>
          <div class="item">Item 16</div>
          <div class="item">Item 17</div>
          <div class="item">Item 18</div>
          <div class="item">Item 19</div>
          <div class="item">Item 20</div>
          <div class="item">Item 21</div>
          <div class="item">Item 22</div>
          <div class="item">Item 23</div>
          <div class="item">Item 24</div>
          <div class="item">Item 25</div>
          <div class="item">Item 26</div>
          <div class="item">Item 27</div>
          <div class="item">Item 28</div>
          <div class="item">Item 29</div>
          <div class="item">Item 30</div>
          <div class="item">Item 31</div>
          <div class="item">Item 32</div>
          <div class="item">Item 33</div>
          <div class="item">Item 34</div>
          <div class="item">Item 35</div>
          <div class="item">Item 36</div>
          <div class="item">Item 37</div>
          <div class="item">Item 38</div>
          <div class="item">Item 39</div>
          <div class="item">Item 40</div>
        
      </div>
    ...

CSS

/* Styles go here */

body {
  margin: 0;
}

.modal {
  height: 100%;
  width: 100%;
  background: #e9f0f6;
  overflow: hidden;
}

.modal-title {
  background: #FF5722;
  height: 52px;
  text-align: center;
  color: white;
  font-size: 1.40em;
  line-height:  52px;
  position: fixed;
  width: 100%;
}

.modal-content {
  height: auto;
  margin-top: 78px;
}

.button-group {
  display: flex;
  top: 52px;
  position: fixed;
  width: 100%;
}

.button.selected {
  background: #03A9F4;
  color: white;
}

.button {
  flex: 1;
  background: #2196F3;
  color: white;
  height: 26px;
  text-align: center;
  line-height:  26px;
  cursor: pointer;
}

.list {
  overflow-y: scroll;
  height: 100%;
}

.item {
  text-align: center;
  font-size: 1.40em;
  padding: 10px;
}