main.js

const colorPickers = document.querySelectorAll('.colors')

const mondrainBlock = document.querySelectorAll('.mondrian div')

colorPickers.forEach((color) => {
  color.addEventListener('click', () => {
    let style = getComputedStyle(color)
    let paint = style.backgroundColor
    color.classList.toggle('outline')

    console.log(paint)

    mondrainBlock.forEach((block) => {
      block.addEventListener('click', () => {
        block.style.backgroundColor = paint
      })
    })
  })
})

dragElement(document.getElementById('toolbar'))
function dragElement(elmnt) {
  var pos1 = 0,
    pos2 = 0,
    pos3 = 0,
    pos4 = 0
  if (document.getElementById(elmnt.id + 'toolbar')) {
    // if present, the header is where you move the DIV from:
    document.getElementById(elmnt.id + 'toolbar').onmousedown = dragMouseDown
  } else {
    // otherwise, move the DIV from anywhere inside the DIV:
    elmnt.onmousedown = dragMouseDown
  }

  function dragMouseDown(e) {
    e = e || window.event
    e.preventDefault()
    // get the mouse cursor position at startup:
    pos3 = e.clientX
    pos4 = e.clientY
    document.onmouseup = closeDragElement
    // call a function whenever the cursor moves:
    document.onmousemove = elementDrag
  }

  function elementDrag(e) {
    e = e || window.event
    e.preventDefault()
    // calculate the new cursor position:
    pos1 = pos3 - e.clientX
    pos2 = pos4 - e.clientY
    pos3 = e.clientX
    pos4 = e.clientY
    // set the element's new position:
    elmnt.style.top = elmnt.offsetTop - pos2 + 'px'
    elmnt.style.left = elmnt.offsetLeft - pos1 + 'px'
  }

  function closeDragElement() {
    // stop moving when mouse button is released:
    document.onmouseup = null
    document.onmousemove = null
  }
}