Add space before and after first and last grid items

Question

My question is identical to this question, but the given solution does not work.

Here is a codepen of what I\'m working with.

I\'ve tried two different approache

Answer 1

One idea to change the width of before is to define a column template like below that will force the width of the first element only then the other will follow the grid-auto-columns. Basically we define an explicit grid with 1 column then the browser will add more column as needed to create the implicit grid:

:root {
  --gap: 25px;
}

body {
  width: 100vw;
  overflow-x: hidden;
  margin: 0
}

#c {
  width: 100%;
  height: 50px;
  overflow-x: auto;
  display: grid;
  grid-gap: 20px;
  grid-template-columns:1px;
  grid-auto-flow: column;
  grid-auto-columns: calc(calc(100% - calc(var(--gap) * 2)) / 1.5);
  border: solid red 1px;
}

/* second approach */
#c::before {
  content: '';
}

#c::after {
  content: '';
  width: 1px; /* works out to about 25px or var(--gap) */
}

.i {
  /*width: 100%; not needed*/
  height: 25px;
  /*display: inline-block; not needed*/
}

.i:nth-child(odd) {
  background: skyblue;
}

.i:nth-child(even) {
  background: pink;
}

<div id='c'>
  <div class='i'>1</div>
  <div class='i'>2</div>
  <div class='i'>3</div>
  <div class='i'>4</div>
  <div class='i'>5</div>
  <div class='i'>6</div>
  <div class='i'>7</div>
  <div class='i'>8</div>
  <div class='i'>9</div>
  <div class='i'>10</div>
  <div class='i'>11</div>
  <div class='i'>12</div>
  <div class='i'>13</div>
  <div class='i'>14</div>
  <div class='i'>15</div>
  <div class='i'>16</div>
  <div class='i'>17</div>
  <div class='i'>18</div>
  <div class='i'>19</div>
  <div class='i'>20</div>
  <div class='i'>21</div>
  <div class='i'>22</div>
  <div class='i'>23</div>
  <div class='i'>24</div>
</div>

Answer 2

This is another one of those instances where flexbox may provide a simpler, easier and more effective solution that grid.

:root {
  --gap: 25px;
}

#c {
  display: flex;
  overflow-x: auto;
  height: 50px;
  border: solid red 1px;
}

.i {
  height: 25px;
  flex: 0 0 calc(calc(100% - calc(var(--gap) * 2)) / 1.5); /* fg, fs, fb */
}

#c::before {
  content: '';
  flex: 0 0 var(--gap);
}

.i {
  margin-right: 20px;
}

#c::after {
  content: '';
  flex: 0 0 calc(var(--gap) - 20px); /* gap less margin */
}

.i:nth-child(odd)  { background: skyblue; }
.i:nth-child(even) { background: pink; }
body               { margin: 0; }
*                  { box-sizing: border-box; }

<div id='c'>
  <div class='i'>1</div>
  <div class='i'>2</div>
  <div class='i'>3</div>
  <div class='i'>4</div>
  <div class='i'>5</div>
  <div class='i'>6</div>
  <div class='i'>7</div>
  <div class='i'>8</div>
  <div class='i'>9</div>
  <div class='i'>10</div>
  <div class='i'>11</div>
  <div class='i'>12</div>
  <div class='i'>13</div>
  <div class='i'>14</div>
  <div class='i'>15</div>
  <div class='i'>16</div>
  <div class='i'>17</div>
  <div class='i'>18</div>
  <div class='i'>19</div>
  <div class='i'>20</div>
  <div class='i'>21</div>
  <div class='i'>22</div>
  <div class='i'>23</div>
  <div class='i'>24</div>
</div>

You may also want to consider a transparent border for start- and end-side spacing. Last margin / padding collapsing in flexbox / grid layout