<div class="store">
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
  <div class="food-item"></div>
</div>


<!--  -->

<div class="inventory-grid">
</div>
.store{
  width: 100%;
  height: 100%;
  padding: calc( 1 * var(--display-unit) );
}

.food-item{
  width: calc( 1 * var(--display-unit) );
  height: calc( 1 * var(--display-unit) );
  outline: 1px solid black;
}

















/* =========================== */
/* Preset */

:root{
  --display-unit: 40px;
}

html {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
}

body * {
  display: flex;
  overflow: hidden;
  box-sizing: border-box;
}

body{
  width: calc( 9 * var(--display-unit) );
  height: calc( 6 * var(--display-unit) );
  outline: 2px black solid;
  position: relative;
}

.inventory-grid{
  --grid-inner-size: calc( var(--display-unit) - 1px );
  --grid-size: calc( var(--display-unit) );
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-image: repeating-linear-gradient(red, transparent 1px var(--grid-inner-size), red), repeating-linear-gradient(90deg, red, transparent 1px var(--grid-inner-size), red var(--grid-inner-size));
  background-size: var(--display-unit) var(--display-unit);
  opacity: 20%;
}

External CSS

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External JavaScript

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