Reducing gap between heading and paragraph

Question

I've coded a blog website which is functioning absolutely fine and doing what I want it to - I'd say I'm about average with CSS, but for the life of me I can't figure out why there's a huge gap between my blog title and summary / date posted below it. I want them to essentially have no margin or gap between them, but obviously not be overflowing.

However, whenever I set the margin to 0, it doesn't reduce the gap. I've tried playing with sizes, but on the whole I want to keep them auto height sized where possible for mobile responsiveness, and reducing code.

Here's an example:

h1 {
  font-size: 8rem;
  letter-spacing: 0.5px;
  color: #ff4766;
}

h2 {
  font-size: 3rem;
  letter-spacing: 0.5px;
  color: ##ff4766;
}

h3 {
  font-size: 2rem;
  letter-spacing: 0.5px;
  color: #ff4766;
}

h4 {
  color: #fff;
}

p {
  font-size: 1rem;
  letter-spacing: 0.5px;
  color: #fff;
}

a {
  font-size: 0.8rem;
  letter-spacing: 0.5px;
  text-decoration: none;
  color: #fff;
}

body {
  margin: 0;
  padding: 0;
  font-family: 'Helvetica', sans-serif;
  box-sizing: border-box;
  background-color: #3b353a;
}


.homepage-blog-section {
  height: auto;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
}

.homepage-blog-container {
  height: 90%;
  width: 90%;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
}

.homepage-blog-post {
  height: auto;
  width: 50%;
  display: flex;
  align-items: center;
  flex-direction: column;
  margin: 40px 0;
}

.homepage-blog-title {
  height: auto;
  width: 100%;
}

.homepage-blog-details {
  height: auto;
  width: 100%;
}

.homepage-blog-details p {
  color: #f9f9f9;
  font-style: italic;
  font-weight: 200;
  font-size: 0.8rem;
}

<section class="homepage-blog-section">
      <div class="homepage-blog-container">
        <div class="homepage-blog-post">
          <div class="homepage-blog-title">
            <a href="">
            <h3>
              Show 
            </h3>
            </a>
          </div>
          <div class="homepage-blog-details">
            <p>
              Test summary
            </p>
            <p>
              Test date
            </p>
          </div>
        </div>
      </div>
    </section>

As you can see when you run that code there's a big gap between the title and the summary/date below it. I've considered putting them into the same div, but to be honest I don't massively want to do that - and it doesn't work exactly how I was hoping.

I'm wanting there to be a similar gap between the title and summary, as there is with the summary and date. I've tried minus margins but that breaks down eventually on smaller devices - and like I said, hoping to keep this code as clean as possible without it being too fiddly.

Is there something obvious I'm missing??