CSS: Why aren't these responsive squares totally square? [duplicate]

Question

I'm trying to make a grid of resizable squares with some text inside them. Here's the code:

/* Dirty quick CSS reset */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.container {
  display: flex;
  flex-flow: column;
  flex: 1;
  background: aliceblue;
}

.row {
  display: flex;
  flex: 1;
}

.square {
  border: 1px solid black;
    
  width: 14.2857%; /* 100% / 7 */
  font-size: 18px;
  padding: 8px;
  
  /* square-width - font-size - padding-top */
  padding-bottom: calc(14.2857% - 18px - 8px);
}

<div class="container">
  <div class="row">
    <div class="square">1</div>
    <div class="square">2</div>
    <div class="square">3</div>
    <div class="square">4</div>
    <div class="square">5</div>
    <div class="square">6</div>
    <div class="square">7</div>
  </div>
</div>

As we can see, there's a row of squares that adapt to the size of the window. The problem is that if we inspect them, we see that they aren't totally squares (they are about 3px taller than wide). It gets worse if we increase the font-size, and as far as I know, the maths is correct.

What's going on here? Why am I getting those extra pixels?

Answer 1

I encountered this problem a while ago, and was able to solve it through this solution by using Pseudo element

/* Dirty quick CSS reset */

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

.container {
  display: flex;
  flex-flow: column;
  flex: 1;
  background: aliceblue;
}

.row {
  display: flex;
  flex: 1;
}

.square {
  border: 1px solid black;
  width: 14.2857%;
  /* 100% / 7 */
  font-size: 18px;
  padding: 8px;
}

.square:before {
  content: '';
  float: left;
  padding-top: 100%;
}

<div class="container">
  <div class="row">
    <div class="square">1</div>
    <div class="square">2</div>
    <div class="square">3</div>
    <div class="square">4</div>
    <div class="square">5</div>
    <div class="square">6</div>
    <div class="square">7</div>
  </div>
</div>

Answer 2

The exact calculation should be (14.2857% - 8px - 2px - Lpx) we remove the padding-top and the border and the line-height (not the font-size), so you should know the value of the line-height or you set it:

/* Dirty quick CSS reset */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.container {
  display: flex;
  flex-flow: column;
  flex: 1;
  background: aliceblue;
}

.row {
  display: flex;
  flex: 1;
}

.square {
  border: 1px solid black;
    
  width: 14.2857%; /* 100% / 7 */
  font-size: 18px; 
  line-height:1em; /*equal to font-size*/
  padding: 8px;
  
  /* square-width - font-size - padding-top */
  padding-bottom: calc(14.2857% - 8px - 2px - 18px);
}

<div class="container">
  <div class="row">
    <div class="square">1</div>
    <div class="square">2</div>
    <div class="square">3</div>
    <div class="square">4</div>
    <div class="square">5</div>
    <div class="square">6</div>
    <div class="square">7</div>
  </div>
</div>

If we refer to the documentation the line-height is the value that define the height of the lines and the default value is set to normal:

The line-height CSS property sets the amount of space used for lines, such as in text.

And

normal

Depends on the user agent. Desktop browsers (including Firefox) use a default value of roughly 1.2, depending on the element's font-family.

As you can see the line-height is not necessarily equal to font-size