JSFiddle - React, Tailwind, and code Playground

HTML

<div class="SplitContainer">
  <div class="ContentPane">
    Some Text
  </div>
  <div class="Divider"></div>
  <div class="ContentPane">
    Other Text
  </div>
</div>

CSS

.SplitContainer {
  background: #eee;
  height: 300px;
  position: relative;
}
.SplitContainer.dragging {
  cursor: move;
}

.ContentPane {
  background: white;
  border: 1px solid #ccc;
  bottom: 0px;
  box-sizing: border-box;
  display: block;
  overflow: hidden;
  position: absolute;
  top: 0px;
}

.Divider {
  background: #ddd;
  bottom: 0px;
  cursor: move;
  display: block;
  position: absolute;
  top: 0px;
  width: 5px;
}

JavaScript

// Variable Setup
var splitContainerWidth = $('.SplitContainer').width();
var divider = $('.Divider');
var firstContentPane = $('.SplitContainer .ContentPane').eq(0);
var secondContentPane = $('.SplitContainer .ContentPane').eq(1);
var contentPaneMinWidth = 50;
var dividerWidth = divider.width();
firstContentPane.css('left', '0px');
secondContentPane.css('right', '0px');
var lastDividerX = 0;
var isDragging = false;
var dragStartX = 0;
var splitContainerPageX = $('.SplitContainer').offset().left;

// Resize the content panes based on divider x position
function resize(dividerX) {
  lastDividerX = dividerX;
	firstContentPane.css('right', splitContainerWidth - dividerX);
  divider.css('left', dividerX);
  secondContentPane.css('left', dividerX+dividerWidth);
}
// Initial Divider Position
resize(200);

// Attach events to divider for resizing
$('.Divider').on('mousedown', function(e) {
  $('.SplitContainer').addClass('dragging');
	isDragging = true;
});
$(document).on('mouseup', function() {
  $('.SplitContainer').removeClass('dragging');
  isDragging = false;
});
$(document).on('mousemove', function(e) {
  if (isDragging) {
  	resize(Math.min(splitContainerPageX + splitContainerWidth - dividerWidth - contentPaneMinWidth, Math.max(contentPaneMinWidth, e.pageX - splitContainerPageX - (dividerWidth/2))));
  }
});

// Window resize
$(window).on('resize', function() {
  splitContainerPageX = $('.SplitContainer').offset().left;
  splitContainerWidth = $('.SplitContainer').width();
  resize(Math.min(lastDividerX, splitContainerPageX + splitContainerWidth - dividerWidth - contentPaneMinWidth));
});