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HTML

              
                <p role="toolbar" aria-label="Node tools" aria-hidden="true" class="toolbar">
  <button type="button" data-js="promoteSibling">&laquo; Move left</button>
  <button type="button" data-js="demoteSibling">Move right &raquo;</button>
  <button type="button" data-js="addChild">+ Add new</button>
  <button type="button" data-js="deleteNode">
    &times; Delete
    <ins role="alert" aria-hidden="true" class="confirm" aria-label="Please confirm deletion">Are you sure? (press again to continue)</ins>
    <ins role="alert" aria-hidden="true" class="root" aria-label="You can't delete root">You can't delete the root node</ins>
  </button>
  <button type="button" data-js="editName">✎ Edit name</button>
</p>

<details>
  <summary>Customise your tree view</summary>
  <div class="grid">
    <p><label for="line-color">Line colour</label> <input type="color" id="line-color" name="line-color" value="#666"></p>
    <p><label for="line-width">Line width</label> <input type="range" id="line-width" name="line-width"  value="1" min="1" max="10"></p>
    <p><label for="gutter">Gutters</label> <input type="range" id="gutter" name="gutter" value="5" min="1" max="10"></p>
  </div>
</details>
  
<ul class="tree">
  <li>
    <button type="button" aria-pressed="false" data-js="node">Home</button>
    <ul>
      <li><button type="button" aria-pressed="false" data-js="node">One</button></li>
      <li><button type="button" aria-pressed="false" data-js="node">Two</button></li>
      <li><button type="button" aria-pressed="false" data-js="node">Three</button></li>
    </ul>
  </li>
</ul>
              
            
!

CSS

              
                // These are CSS variables, so I can tinker with them in JavaScript.
:root {
  --line-color: #666;
  --line-width: .1em;
  --gutter: .5em;
}

body {
  font-family: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Oxygen-Sans,Ubuntu,Cantarell,"Helvetica Neue",sans-serif;
}

*, *:before, *:after {box-sizing: border-box;}

.tree {
  margin: 0 0 calc(var(--gutter) * 2);
  text-align: center;
  &, & ul, & li {
    list-style: none;
    margin: 0;
    padding: 0;
    position: relative;
  }
  &, & ul {display: table;}
  & ul {width: 100%;}
  & li {
    display: table-cell;
    padding: var(--gutter) 0;
    vertical-align: top;
  }
  /* _________ */
  & li:before {
    content: "";
    left: 0;
    outline: solid calc(var(--line-width) /2) var(--line-color);
    position: absolute;
    right: 0;
    top: 0;    
  }
  & li:first-child:before {left:  50%;}
  & li:last-child:before  {right: 50%;}
  & button {
    border-radius: .2em;
    margin: 0 calc(var(--gutter) / 2) var(--gutter);
    // The user might delete all of the text, causing the button to shrink
    min-height: 2.1em;
    position: relative;
    z-index: 1;
  }
  & [contenteditable] {cursor: text;}
  & .selected {
    border-color: #900;
    border-style: dashed;
    -webkit-box-shadow: 0 0 var(--gutter) var(--line-width) rgba(153,0,0,.3);
       -moz-box-shadow: 0 0 var(--gutter) var(--line-width) rgba(153,0,0,.3);
            box-shadow: 0 0 var(--gutter) var(--line-width) rgba(153,0,0,.3);
  }
  /* | */
  & ul:before,
  & button:before {
    outline: solid calc(var(--line-width) / 2) var(--line-color);
    content: "";
    height: var(--gutter);
    left: 50%;
    position: absolute;
    // This fixes the hack in the previous version
    top: calc(calc(-1 * var(--gutter)) - calc(var(--line-width) / 2));
  }
  /* The root node doesn't connect upwards */
  & > li {margin-top: 0;}
  & > li:before, & > li:after, & > li > button:before {outline: none;}  
}

// The names in the tree
button {
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
  background: #fff;
  border: solid var(--line-width) var(--line-color);
  cursor: pointer;
  font-size: 1em;
  line-height: 1.2em;
  padding: .4em 1em;
  position: relative;
  &:focus, &:hover {
    outline: .1em dotted var(--line-color);
    outline-offset: -.5em;
  }
}
input[type="range"] {
  display: block;
  width: 100%;
}
input[type="color"] {
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
  border: none;
  cursor: pointer;
  display: block;
  height: 2em;
  padding: 0;
  vertical-align: middle;
  width: 100%;
}

.toolbar {
  background: #ccc;
  font-size: .9em;
  left: 0;
  margin: 0;
  padding: var(--gutter);
  position: fixed;
  right: 0;
  text-align: center;
  top: 0;
  transform: translate(0,-100%);
  transition: all .2s ease;
  z-index: 2;
}
.toolbar.show {
  transform: translate(0,0);
}

// Tooltip
ins {
  background: #fff;
  border: solid calc(var(--line-width) /2) var(--line-color);
  display: inline-block;
  font-size: .8em;
  left: -1em;
  margin: 1em 0 0;
  padding: .2em .5em;
  position: absolute;
  right: -1em;
  text-decoration: none;
  top: 100%;
  
  // Speech tick
  &:before, &:after {
    border: solid 1em transparent;
    border-top: none;
    content: "";
    left: 50%;
    position: absolute;
    transform: translate(-50%,0);
  }
  &:before {
    border-bottom-color: var(--line-color);
    bottom: 100%;
  }
  &:after  {
    bottom: calc(100% - var(--line-width));
    border-bottom-color: #fff;
  }
}
// Hide
ins {
  opacity: 0;
  transition: all .2s ease;
  transform: scale(0,0);

}
// Show
.js-confirm .confirm, .js-root .root {
  opacity: 1;
  transform: scale(1,1);
}

// Tiny grid
.grid {
  display: flex;
  width: 100%;
 & > * {
    flex: 1;
    margin-left: .5em;
    margin-right: .5em;
  }
}
              
            
!

JS

              
                var root         = document.documentElement,
    toolBar      = document.querySelector('[role="toolbar"]'),
    colorInput   = document.querySelector('#line-color'),
    lineInput    = document.querySelector('#line-width'),
    gutterInput  = document.querySelector('#gutter'),
    alertRoot    = document.querySelector('[data-js="deleteNode"] .root'),
    alertConfirm = document.querySelector('[data-js="deleteNode"] .confirm'),
    // Used for naming new nodes
    nodeNames    = ["Dolor", "Amet", "Consectetur", "Adipiscing", "Elit", "Nunc", "Sagittis", "Pretium", "Convallis", "Curabitur", "Turpis", "Velit", "Vitae", "Rutrum",  "Sapien", "Orci", "Tempor", "Elementum",  "Risus", "Etiam", "Ante", "Hendrerit", "Malesuada", "Donec", "Porttitor", "Eget", "Libero", "Pharetra", "Aliquam", "Mattis", "Massa", "Porta", "Morbi", "Augue", "Lectus", "Tellus", "Facilisis", "Tincidunt", "Suspendisse", "Eros", "Magna", "Consequat", "Sollicitudin", "Vestibulum", "Egestas", "Quis", "Lacus", "Molestie",  "Scelerisque", "Nullam", "Tortor", "Aenean", "Pulvinar", "Odio", "Placerat", "Fringilla", "Neque"];

// All the button and body clicks are intercepted here.
document.addEventListener('click', function (e) {
  var clickType = e.target.getAttribute('data-js');
  // User has selected a node
  if (clickType === 'node') {
    selectNode(e);
  } else if (clickType !== '' && clickType !== null) {
    // Buttons within the toolbar, at the top of the page
    if      (clickType === 'promoteSibling') promoteSibling();
    else if (clickType === 'demoteSibling')  demoteSibling();
    else if (clickType === 'editName')       editName();
    else if (clickType === 'deleteNode')     deleteNode(e);
    else if (clickType === 'addChild')       addChild();
  } else {
    // User has clicked outside of a node
    deselectNodes();
    hideToolbar();
  }
});

// Customise views events
colorInput.addEventListener('change', lineColor);
lineInput.addEventListener('change', lineWidth);
gutterInput.addEventListener('change', gutterWidth);

function lineColor(e) {
  root.style.setProperty('--line-color', e.target.value);
}
function lineWidth(e) {
  root.style.setProperty('--line-width', (e.target.value / 10) + 'em');
}
function gutterWidth(e) {
  root.style.setProperty('--gutter', (e.target.value / 10) + 'em');
}

// Allows the user to reorder the tree with the keyboard
root.addEventListener('keydown', function (e) {
  var keyPress;
  // New method vs. old method
  if (e.key) keyPress = e.key;
  else       keyPress = e.which;
  // If the user is editing a node name, they might need to use the arrow keys As God Intended
  if (e.target.getAttribute('contenteditable')) {
    if (keyPress === ' ' || keyPress === '32') {
      insertTextAtCursor(' ');
    }
  } else {
    if (keyPress === 'ArrowRight' || keyPress === '37') {
      demoteSibling();
    } else if (keyPress === 'ArrowLeft' || keyPress === '39') {
      promoteSibling();
    }
  }
  // This is useful whether the user is editing the button or not
  if (keyPress === 'ArrowDown' || keyPress === '40') {
    addChild();
  }
});

// Deselects all other nodes, selects the current node and hoyks in the toolber
function selectNode(e) {
  var clicker = e.target;
  // Hang on - do we need to do anything?
  if (clicker.getAttribute('aria-pressed') === 'false') {
    deselectNodes();
    clicker.setAttribute('aria-pressed', 'true');
    clicker.classList.add('selected');
    showToolbar();   
  }
}

// Bit of cleanup, after the user has finished editing the tree.
function deselectNodes() {
  // This needs to run from scratch as new nodes might have been added
  var selectedBtns = [...document.querySelectorAll('.tree [aria-pressed="true"]')],
      btnDelete = document.querySelector('[data-js="deleteNode"]'),
      editBtns = [...document.querySelectorAll('.tree [contenteditable]')];
  // I mean, in theory, there should only be one selected button, but, you know, bugs...
  for (var i = 0; i < selectedBtns.length; i++) {
    selectedBtns[i].setAttribute('aria-pressed', 'false');
    selectedBtns[i].classList.remove('selected');
  }
  // Bit of cleanup, in case the user noped out of deleting a node
  if (btnDelete.classList.contains('js-confirm')) {
    btnDelete.classList.remove('js-confirm');
    alertConfirm.setAttribute('aria-hidden','true');
  }
  if (btnDelete.classList.contains('js-root')) {
    btnDelete.classList.remove('js-root');
    alertRoot.setAttribute('aria-hidden','true');
  }
  // Checks for new nodes which are editable, then turns them off.
  for (var i = 0; i < editBtns.length; i++) {
    editBtns[i].removeAttribute('contenteditable');
  }
}

function showToolbar() {
  toolBar.removeAttribute('aria-hidden');
  toolBar.classList.add('show');
}

function hideToolbar() {
  toolBar.setAttribute('aria-hidden','true');
  toolBar.classList.remove('show');
}

// Moves the sibling to the left
function promoteSibling() {
  if (document.querySelector('.tree .selected')) {
    var favouriteChild = document.querySelector('.tree .selected').parentNode,
        elderChild = favouriteChild.previousElementSibling;
    // Does this selected element have anywhere to go?
    if (elderChild) {
      favouriteChild.parentNode.insertBefore(favouriteChild,elderChild);
    }    
  }
}

// Moves the sibling to the right
function demoteSibling() {
  if (document.querySelector('.tree .selected')) {
    var chosenChild = document.querySelector('.tree .selected').parentNode,
        youngerChild = chosenChild.nextElementSibling;
    // Does this selected element have anywhere to go?
    if (youngerChild) {
      chosenChild.parentNode.insertBefore(youngerChild,chosenChild);
    }    
  }
}

// Allows the user to rename existing nodes
function editName() {
  var chosenChild = document.querySelector('.tree .selected');
  chosenChild.setAttribute('contenteditable', 'true');
  chosenChild.focus();
}

// Removes the node and it's children
function deleteNode(e) {
  var chosenChild  = document.querySelector('.tree .selected'),
      delButton    = e.target,
      isRoot       = chosenChild.parentNode.parentNode.classList.contains('tree');
  
  // Is the user trying to delete the root node?
  if (isRoot) {
    delButton.classList.add('js-root');
    alertRoot.removeAttribute('aria-hidden');
  }
  // Has the user clicked the delete button once already?
  else if (delButton.classList.contains('js-confirm')) {
    // Is there more than one sibling?
    if (chosenChild.parentNode.parentNode.childElementCount > 1) {
      chosenChild.parentNode.remove();
    } else { // Remove the whole list
      chosenChild.parentNode.parentNode.remove();
    }
    deselectNodes();
    hideToolbar();
  } else {
    delButton.classList.add('js-confirm');
    alertConfirm.removeAttribute('aria-hidden');
  }
}

// Adds a new node under the current node
function addChild() {
  if (document.querySelector('.tree .selected')) {
    var chosenNode = document.querySelector('.tree .selected').parentNode,
        listItem = document.createElement('li');
    listItem.innerHTML = '<button type="button" aria-pressed="false" data-js="node" contenteditable="true">' +
      nodeNames[Math.round(Math.random() * (nodeNames.length - 1))] + '</button>';
    // The current node already has kids
    if (chosenNode.querySelector('ul')) {
      var chosenKids = chosenNode.querySelector('ul');
      chosenKids.appendChild(listItem);
      chosenKids.lastChild.querySelector('button').focus();
    } else { // The current node has no kids
      var newDad = document.createElement('ul');
      newDad.appendChild(listItem);
      chosenNode.appendChild(newDad);
      chosenNode.lastChild.querySelector('button').focus();
    }    
  }
}

// Because each node is a button tag, the space bar event is captured, when the user is editing.
// This is used as a work-around.
function insertTextAtCursor(text) {
    var sel, range;
    if (window.getSelection) {
        sel = window.getSelection();
        if (sel.getRangeAt && sel.rangeCount) {
            range = sel.getRangeAt(0);
            range.deleteContents();
            range.insertNode( document.createTextNode(text) );
        }
    } else if (document.selection && document.selection.createRange) {
        document.selection.createRange().text = text;
    }
}
              
            
!
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