Conclusion jusqu'à présent :

const container = document.getElementById('container');

//draws the board
emptyElementAndFillWithColumns(container, 100);
//sets some columns randomly as .square
addRandomSquares(container);

//initializes the dashboard with the value coming from the css custom props
let columnsGap = parseInt(getCssCustomProp('col-gap'));
let columnsWidth = parseInt(getCssCustomProp('col-width'));
document.getElementById('gap').value = columnsGap;
document.getElementById('width').value = columnsWidth;
document.getElementById('width').dispatchEvent(new Event('change'));
document.getElementById('cols').value = Math.trunc(container.offsetWidth / (columnsWidth+columnsGap));

//input#width change event handler
document.getElementById('width')
  .addEventListener('change', event => {
    const width = parseInt(event.target.value);
    const newCols = Math.trunc(container.offsetWidth / (width+columnsGap));
    setCssCustomProp(container, 'col-width', `${width}px`);
    document.getElementById('cols').value = newCols;
  });

//input#cols change event handler
document.getElementById('cols')
  .addEventListener('change', event => {
    const cols = parseInt(event.target.value);
    const newWidth = Math.trunc(container.offsetWidth / cols) - columnsGap;
    setCssCustomProp(container, 'col-width', `${newWidth}px`);
    document.getElementById('width').value = newWidth;
  });
  
//input#gap change event handler
document.getElementById('gap')
  .addEventListener('change', event => {
    const gap = parseInt(event.target.value);
    setCssCustomProp(container, 'col-gap', `${gap}px`);
    columnsGap = gap;
  });
  
//input#toggle-dots change event handler
document.getElementById('toggle-dots')
  .addEventListener('change', event => {
    container.classList.toggle('hide-dots');
  });
  
//input#toggle-counters change event handler
document.getElementById('toggle-counters')
  .addEventListener('change', event => {
    container.classList.toggle('hide-counters');
  });

//sets the --propName custom property at the style of target
function setCssCustomProp(target, propName, value){
  target.style.setProperty(`--${propName}`, `${value}`);
}

//gets the --propName custom property value from the rule set on :root
function getCssCustomProp(propName){
  const propValue =
  getComputedStyle(document.documentElement).getPropertyValue(`--${propName}`);
  return propValue;
}

//resets the container and appends a count number of columns
function emptyElementAndFillWithColumns(target, count){
  for (i = 0; i  {
    if (Math.random() >= 0.5)
      column.classList.add('square');
  })
}

:root {
  --col-width: 100px;
  --col-gap: 1px;
}

*,
*::after,
*::before {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: sans-serif;
}

.row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--col-gap);
  counter-reset: itemnr;
}

.column {
  position: relative;
  display: flex;
  flex-wrap: wrap;
  width: var(--col-width);
  height: var(--col-width);
  padding: 4px;
  outline: var(--col-gap) solid gray;
}

.column.square::after {
  position: absolute;
  content: '';
  background-color: red;
  
  width: 50%;
  aspect-ratio: 1/1;
  border-radius: 100%;
  
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%); 
}

.dashboard {
  position: fixed;
  right: 1rem;
  top: 2rem;
  border: solid darkgray;
  padding: 1em;
  z-index: 100;
  background: gray;
  color: white;
  font-weight: 600;
  font-size: 1.2rem;
  opacity: .9;
}

.dashboard > *{
  display: grid;
  grid-template-columns: 1fr auto;
  width: 100%;
  gap: 1em;
}

.dashboard label{
}

.dashboard input[type="number"] {
  width: 5em;
  cursor: pointer;
}

.dashboard input[type="checkbox"] {
  width: 1rem;
  line-height: 1rem;
  cursor: pointer;
}

#container.hide-dots .square::after{
  display: none;
}

#container.hide-counters .column::before{
  display: none;
}

small{
  grid-column: 1 / -1;
  font-size:.8rem;
  text-align: center;
  width: 100%;
  margin-bottom: 1rem;
}

.column::before{
  position: absolute;
  counter-increment: itemnr; 
  content: counter(itemnr);
  font-size: .8rem;
  z-index: 10;
  font-weight: 600;
}

  

  
  




  

    column width (px):
    
  
  

    columns per row:
    
  
  

    gap between cells (px):
    
  
  

    toggle red dots visibility:
    
  
  

    toggle counter visibility: