How to make a responsive hamburger menu using CSS only?

<nav class="nav">
  <a href="#" class="nav__logo">CompanyLogo</a>

  <!-- focus on this div -->
  <div class="nav__menucontainer">
    <div class="nav__listcontainer" tabindex="0">
      <ul class="nav__menu" id="navmenu">
        <li class="nav__item">
          <a href="#" class="nav__link">About</a>
        </li>
        <li class="nav__item">
          <a href="#" class="nav__link">Projects</a>
        </li>
        <li class="nav__item">
          <a href="#" class="nav__link">Contact</a>
        </li>
        <li class="nav__item">
          <a href="#" class="nav__link">Blog</a>
        </li>
      </ul>
      <a id="hamburger" href="#navmenu" title="menu" class="nav__hamburger">
        <i class="fa fa-2x fa-hamburger"></i>
      </a>
    </div>
    <a href="#!" title="close menu" class="nav__hamburgerclose"><i class="fa fa-2x fa-times-circle"></i></a>
  </div>

</nav>

/* most part is for styling, and you can safely ignore it */
/* comments are placed wherever necessary */

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  background-color: #f5f5f5;
  margin: 0;
  font-family: sans-serif;
}

a {
  text-decoration: none;
}

/* --- You will know what this is --- */
#blobSvg {
  max-width: 520px;
}

.nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: fixed;
  width: 100%;
  background-color: rgba(51, 51, 51, 0.85);
  color: #efefef;
  z-index: 5;
  padding: 1rem;
}

.nav__logo {
  text-decoration: none;
  color: inherit;
  font-weight: 700;
  font-size: 1.5rem;
}

.nav__menucontainer {
  position: relative;
}

.nav__hamburger {
  color: inherit;
  min-width: 32px;
  min-height: 32px;
  transition: opacity 80ms linear;
  /* hiding the hamburger icon on large screen sizes */
  display: none;
  opacity: 0;
}

.nav__hamburgerclose {
  color: inherit;
  position: absolute;
  top: 0;
  min-width: 32px;
  min-height: 32px;
  transition: opacity 150ms linear;
  /*   hiding the close icon and... */
  display: none;
  opacity: 0;
  z-index: -1; /* pushing it behind the hamburger icon so that hamburger icon can be clicked */
}

.nav__menu {
  padding: 0;
  margin: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  font-size: 0.95rem;
  font-weight: 500;
}

.nav__item {
  margin-right: 1rem;
}

.nav__link {
  color: inherit;
  text-decoration: none;
  width: 100%;
}

.nav__link:hover,
.nav__link:focus-visible {
  box-shadow: 0 4px 0 -1px #a2e718;
}

/* ----- smaller screen sizes ----- */
@media (max-width: 520px) {
  .nav__hamburger {
    /* making the hamburger icon visible on smaller screen sizes */
    display: flex;
    opacity: 1;
  }

  .nav__menu {
    /* move menu offscreen */
    opacity: 0;
    position: fixed;
    visibility: none;
    top: -1000px;

    /* just some styles */
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    color: #25310c;
    box-shadow: 0 0 30px rgba(0, 0, 0, 0.19);
    border: 2px solid rgba(255, 255, 255, 0.2); /* part of glass morphism effect */
    border-radius: 2rem 0 2rem 2rem;
    background: rgba(255, 255, 255, 1);
  }

  /* uncomment the line below to activate on hover. */
  /*   .nav__listcontainer:hover .nav__menu, */
  .nav__listcontainer:focus .nav__menu,
  .nav__listcontainer:focus-within .nav__menu {
    position: absolute;
    visibility: visible;
    opacity: 1;
    top: 2rem;
    right: 1.5rem;
  }

  /*   if the browser supports backdrop-filter property, 
  then add it (for the glass morphism effect) */
  @supports (backdrop-filter: blur(10px)) {
    /* uncomment the line below to activate on hover. */
    /*     .nav__listcontainer:hover .nav__menu, */
    .nav__listcontainer:focus .nav__menu,
    .nav__listcontainer:focus-within .nav__menu {
      background: rgba(255, 255, 255, 0.7);
      backdrop-filter: blur(10px);
    }
  }

  .nav__item {
    margin-right: 0;
    padding: 0.5rem 1.5rem;
  }

  .nav__link:hover,
  .nav__link:focus {
    opacity: 0.8;
    color: #121212;
  }

  /*  uncomment the line below to activate on hover. */
  /* NOTE: Hover is not recommended, it will have side effects on this */
  /*   .nav__listcontainer:hover .nav__hamburger, */
  .nav__listcontainer:focus .nav__hamburger,
  .nav__listcontainer:focus-within .nav__hamburger {
    opacity: 0;
    z-index: -1;
  }

  /* uncomment the line below to activate on hover. */
  /* NOTE: Hover is not recommended, it will have side effects on this */
  /*   .nav__listcontainer:hover + .nav__hamburgerclose, */
  .nav__listcontainer:focus + .nav__hamburgerclose,
  .nav__listcontainer:focus-within + .nav__hamburgerclose {
    display: flex;
    opacity: 1;
    z-index: 1;
  }
}

<nav>
   ...
</nav>

<div class="container">
  <!--   svg is placed to see the glass morphism effect -->
  <svg viewBox="0 0 500 500" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="100%" id="blobSvg">
    <defs>
      <linearGradient id="gradient" x1="0%" y1="0%" x2="0%" y2="100%">
        <stop offset="0%" style="stop-color: rgb(255, 95, 109);"></stop>
        <stop offset="100%" style="stop-color: rgb(255, 195, 113);"></stop>
      </linearGradient>
    </defs>
    <path id="blob" d="M365,286Q374,322,337.5,330.5Q301,339,275.5,410.5Q250,482,221.5,415Q193,348,154.5,337.5Q116,327,82,288.5Q48,
                       250,57,197Q66,144,98,93.5Q130,43,190,76Q250,109,304,86Q358,63,361,123.5Q364,184,360,217Q356,250,365,286Z" fill="url(#gradient)"></path>
  </svg>
</div>

.container {
  display: flex;
  flex-direction: column;
  align-items: center; /* centering elements inside .container */
  width: 100%;
  max-width: 720px;
  margin: 0 auto; /* centering container within its parent */
  padding: 2em 1.5em;
  background: #fff;
}