Margin Collapsing in CSS

index.html

<div class="container">
  <h1>Margin collapsing in CSS</h1>
  <!--  Normal container  -->
  <div class="sub-container">
    <div class="box-normal">
      <h2>Normal Container</h2>
      <p class="first-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
      <p class="second-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
    </div>

    <!--  Flexbox container  -->
    <div class="box-flex">
      <h2>Flexbox Container</h2>
      <p class="first-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
      <p class="second-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
    </div>

    <!--  Grid container  -->
    <div class="box-grid">
      <h2>Grid Container</h2>
      <p class="first-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
      <p class="second-para">Lorem ipsum dolor sit amet consectetur adipisicing elit. Eaque illo quod praesentium porro hic voluptatibus ex consequatur. Nam, quisquam excepturi.</p>
    </div>
  </div>
</div>

style.css

@import url("https://fonts.googleapis.com/css2?family=Rowdies:wght@300;400&display=swap");

:root {
  --spacing: 2rem;
}

.box-normal {
  /* NOTHING TO PUT HERE AS
  THIS IS A NORMAL CONTAINER */
}

.box-flex {
  display: flex;
  flex-direction: column;
}

.box-grid {
  display: grid;
}

/* FIRST BIGGER MARGIN */
.first-para {
  margin-bottom: var(--spacing);
}

/* SECOND SMALLER MARGIN */
.second-para {
  margin-top: calc(var(--spacing));
}

/*======================*/
/*=====OTHER STYLES=====*/

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

html,
body {
  height: 100%;
}

body {
  font-family: "Rowdies", cursive;
  line-height: 1.4;
}

p {
  font-weight: 300;
  font-family: sans-serif;
}

.container {
  height: 100%;
  border: 16px ridge #ff6550;
  background: #ffe7e7;
  overflow: auto;
  padding: var(--spacing);
}

.sub-container {
  max-width: 1200px;
  height: 80%;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
  place-items: center;
  gap: var(--spacing);
  margin: calc(var(--spacing) * 1.5) auto;
}

.sub-container > div {
  background: #ea5b4853;
  border-radius: 10px;
}

h1,
h2 {
  text-align: center;
}

h2 {
  margin-bottom: 1rem;
}