Use This Simple Line Of CSS Grid To Make Your Layout Responsive

grid-tips

grid-template-columns: repeat(auto-fit, minmax(min(100%,[base-width]), 1fr));

https://codepen.io/optimisticweb/full/pvjzdjg

HTML
<h1>Responsive Layout</h1>
<h2>Without Using Media Query</h2>
<section class="content-boxes">
  <div class="content-box">1</div>
  <div class="content-box">2</div>
  <div class="content-box">3</div>
  <div class="content-box">4</div>
  <div class="content-box">5</div>
  <div class="content-box">6</div>
  <div class="content-box">7</div>
  <div class="content-box">8</div>
  <div class="content-box">9</div>
  <div class="content-box">10</div>
  <div class="content-box">11</div>
  <div class="content-box">12</div>
</section>

css
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: system-ui, sans-serif;
  font-size: 1rem;
  line-height: 1.7;
  color: #070707;
  background: fixed linear-gradient(transparent, #fff 70%),
    fixed
      repeating-linear-gradient(
        #efefef,
        #efefef 1px,
        transparent 1px,
        transparent 40px
      ),
    fixed
      repeating-linear-gradient(
        to right,
        #efefef,
        #efefef 1px,
        transparent 1px,
        transparent 40px
      )
      #fff;
  padding: 3rem;
}

h1 {
  font-size: clamp(0.5rem, 2vw + 0.5rem, 1.75rem);
  text-align: center;
}

h2 {
  font-size: clamp(0.5rem, 2vw + 0.5rem, 1.25rem);
  font-weight: 600;
  text-align: center;
  margin-block-end: 2rem;
}

.content-boxes {
  display: grid;
  /* grid-template-columns:
    repeat(auto-fit, minmax(200px, 1fr)); */
  /* Magic happens here */
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 200px), 1fr));
  gap: 1rem;
}

.content-box {
  display: flex;
  justify-content: center;
  align-items: center;
  aspect-ratio: 1;
  font-size: 1.25rem;
  outline: 1px dotted #fff;
  outline-offset: -0.5rem;
}

.content-box:nth-child(1),
.content-box:nth-child(7) {
  background-color: #fcc7a1;
}

.content-box:nth-child(2),
.content-box:nth-child(8) {
  background-color: #a6fee6;
}

.content-box:nth-child(3),
.content-box:nth-child(9) {
  background-color: #bda9fa;
}

.content-box:nth-child(4),
.content-box:nth-child(10) {
  background-color: #a3dbf8;
}

.content-box:nth-child(5),
.content-box:nth-child(11) {
  background-color: #fba7e3;
}

.content-box:nth-child(6),
.content-box:nth-child(12) {
  background-color: #a8c6fb;
}