CSS Grid - Highlight cells up to the hovered cell

Question

In a grid, I want to highlight group of cells - a rectangle shape - starting from top left cell up to the cell under the mouse position.

Let's say our grid initially looks like this:

.grid {
  display: grid;
  grid-template-columns: repeat(5, 50px);
  grid-template-rows: repeat(5, 50px);
  gap: 5px;
}

.grid-item {
  display: flex;
  justify-content: center;
  align-items: center;
  background: lightgray;
}

And now the user hovers with the mouse over cell number 18. The grid should look like this now:

.grid {
  display: grid;
  grid-template-columns: repeat(5, 50px);
  grid-template-rows: repeat(5, 50px);
  gap: 5px;
}

.grid-item {
  display: flex;
  justify-content: center;
  align-items: center;
  background: lightgray;
}

.grid-item-blue {
  background: lightblue;
}

I prefer css solution. Is is possible using css only? If not, how would you do this in JS?

user_10698741 · Answer

Here is pure CSS solution with flexbox but too complex.

.grid {
  display: flex;
  flex-wrap: wrap;
  flex-flow: wrap-reverse;
  direction: rtl;
  width: calc(50px*5 + 5px*4);
}

.grid-item {
  width: 50px;
  height: 50px;
  display: flex;
  justify-content: center;
  align-items: center;
  background: lightgray;
  margin-bottom: 5px;
}

.grid-item:not(:nth-child(5n + 1)) {
  margin-right: 5px;
}

.grid-item:nth-child(5n - 4):hover,
.grid-item:nth-child(5n - 4):hover~.grid-item,
.grid-item:nth-child(5n - 3):hover,
.grid-item:nth-child(5n - 3):hover~.grid-item:not(:nth-child(5n + 1)),
.grid-item:nth-child(5n - 2):hover,
.grid-item:nth-child(5n - 2):hover~.grid-item:not(:nth-child(5n + 1)):not(:nth-child(5n + 2)),
.grid-item:nth-child(5n - 1):hover,
.grid-item:nth-child(5n - 1):hover~.grid-item:not(:nth-child(5n + 1)):not(:nth-child(5n + 2)):not(:nth-child(5n + 3)),
.grid-item:nth-child(5n):hover,
.grid-item:nth-child(5n):hover~.grid-item:not(:nth-child(5n + 1)):not(:nth-child(5n + 2)):not(:nth-child(5n + 3)):not(:nth-child(5n + 4))
{
  background: lightblue;
}

user_7148391 · Answer

Here's a pure css Idea if you don't mind nesting the content on more level just to put it over the fake background.

.grid {
    overflow:hidden;
    display: grid;
    grid-template-columns: repeat(5, 50px);
    grid-template-rows: repeat(5, 50px);
    gap: 5px;
}

.grid-item {
    background: lightgray;
    position: relative;
    display: flex;
}

.grid-item>span {
    z-index: 2;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}

.grid-item:hover:before {
    position: absolute;
    content: '';
    background: linear-gradient(to left,#ff000000 0px 50px,#ffffff 50px 55px) 0 0/55px, linear-gradient(to top,lightblue 0px 50px,#ffffff00 50px 55px) 0 0/1px 55px ;
    z-index: 1;
    width: calc(55px * 9);
    height: calc(55px * 9);
    bottom: 0;
    right: 0;
}

user_7353319 · Answer

I think it very hard to do this with pure CSS, especially if you plan to expand this grid. However it can be done with javascript

document.querySelector('.grid').addEventListener("mouseover", function (event) {
    Array.from(this.querySelectorAll('.grid-item')).forEach(node => {
        var nodePosition = node.getBoundingClientRect();
        if (nodePosition.x <= event.clientX && nodePosition.y <= event.clientY) {
            node.classList.add('grid-item-blue')
        }
        else {
            node.classList.remove('grid-item-blue')
        }
    })
});

.grid {
  display: grid;
  grid-template-columns: repeat(5, 50px);
  grid-template-rows: repeat(5, 50px);
  gap: 5px;
}

.grid-item {
  display: flex;
  justify-content: center;
  align-items: center;
  background: lightgray;
}
.grid-item-blue {
  background: lightblue;
}

You can also use debouncing to reduce the number of times the mouseover callback function is triggered.

CSS Grid - Highlight cells up to the hovered cell

3 Answers