:root {
  --screen-width: 320px;
  --screen-height: 560px;
  --header-bg-color: #673AB7;
  --splash-bg-color: #368887;
}

<!-- Main Navigation Menu -->
.nav__toggle {
  display: inline-block;
  position: absolute;
  z-index: 10;
  padding: 0;
  border: 0;
  background: transparent;
  outline: 0;
  right: 15px;
  top: 15px;
  cursor: pointer;
  border-radius: 50%;
  transition: background-color 0.15s linear;
}

.nav__toggle:hover,
.nav__toggle:focus {
  background-color: rgba(0, 0, 0, 0.5);
}

.nav__menu {
  display: flex;
  flex-direction: column;
  justify-content: center;
  height: var(--screen-height);
  position: relative;
  z-index: 5;
  visibility: hidden;
  font-family: "Helvetica", Arial, sans-serif;
  font-size: 14pt;
}

.nav__item {
  opacity: 0;
  transition: all 0.3s cubic-bezier(0.000, 0.995, 0.990, 1.000) 0.3s;
}

.nav__item:nth-child(1) {
  transform: translateY(-40px);
}
.nav__item:nth-child(2) {
  transform: translateY(-80px);
}
.nav__item:nth-child(3) {
  transform: translateY(-120px);
}
.nav__item:nth-child(4) {
  transform: translateY(-160px);
}
.nav__item:nth-child(5) {
  transform: translateY(-200px);
}

<!--
.nav__link {
  color: white;
  display: block;
  text-align: center;
  text-transform: uppercase;
  letter-spacing: 5px;
  font-size: 1.55rem;
  text-decoration: none;
  padding: 1rem;
  font-family: "Helvetica", Arial, sans-serif;
  font-size: 14pt;
} -->

<!-- Link styling -->
.nav__link {
  display: inline-block;
  padding: 10px 14px;
  color: #0b2540;
  text-decoration: none;
  border-radius: 8px;
  font-weight: 600;
  font-size: 15px;
  transition: background-color 120ms ease, transform 120ms ease;
<-- End Link styling -->

.nav__link:hover,
.nav__link:focus {
  outline: 0;
  background-color: rgba(55, 131, 32, 0.8);
}

<!-- SVG Menu Icon -->
.menuicon {
  display: block;
  cursor: pointer;
  color: white;
  transform: rotate(0deg);
  transition: 0.3s cubic-bezier(0.165, 0.840, 0.440, 1.000);
  color: rgba(55, 131, 32, 0.8);
}

.menuicon__bar,
.menuicon__circle {
  fill: none;
  stroke: currentColor;
  stroke-width: 3;
  stroke-linecap: round;
}

.menuicon__bar {
  transform: rotate(0deg);
  transform-origin: 50% 50%;
  transition: transform 0.25s ease-in-out;
}

.menuicon__circle {
  transition: stroke-dashoffset 0.3s linear 0.1s;
  stroke-dashoffset: 144.513; /* circumference of circle with r=23 */
  stroke-dasharray: 144.513;
}

<!-- Circular Splash Background -->
.splash {
  position: absolute;
  top: 40px;
  right: 40px;
  width: 1px;
  height: 1px;
}

.splash::after {
  content: "";
  display: block;
  position: absolute;
  border-radius: 50%;
  background-color: var(--splash-bg-color);
  width: 284vmax;
  height: 284vmax;
  top: -142vmax;
  left: -142vmax;
  transform: scale(0);
  transform-origin: 50% 50%;
  transition: transform 0.5s cubic-bezier(0.755, 0.050, 0.855, 0.060);
  will-change: transform;
}

<!-- Active State -->
.nav:target,
.nav--open > .splash::after {
  transform: scale(1);
}

.nav:target .menuicon,
.nav--open .menuicon {
  color: white;
  transform: rotate(180deg);
}

.nav:target .menuicon__circle,
.nav--open .menuicon__circle {
  stroke-dashoffset: 0;
}

.nav:target .menuicon__bar:nth-child(1),
.nav:target .menuicon__bar:nth-child(4),
.nav--open .menuicon__bar:nth-child(1),
.nav--open .menuicon__bar:nth-child(4) {
  opacity: 0;
}

.nav:target .menuicon__bar:nth-child(2),
.nav--open .menuicon__bar:nth-child(2) {
  transform: rotate(45deg);
}

.nav:target .menuicon__bar:nth-child(3),
.nav--open .menuicon__bar:nth-child(3) {
  transform: rotate(-45deg);
}

.nav:target .nav__menu,
.nav--open .nav__menu {
  visibility: visible;
}

.nav:target .nav__item,
.nav--open .nav__item {
  opacity: 1;
  transform: translateY(0);
}

<!-- Demo Styles -->
body {
  background-color: #D7D7D7;
  font-family: 'Roboto';
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.viewport {
  width: var(--screen-width);
  height: var(--screen-height);
  margin: 0 auto;
  position: relative;
  overflow: hidden;
  background-color: white;
}

.header {
  height: 5rem;
  background-color: var(--header-bg-color);
}

.main {
  padding: 20px;
}

.container {
    display: flex; /* Use flexbox for desktop layout */
}

.pane {
    flex: 1; /* Each pane takes equal space */
    color: red;
}

.gallery {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
  grid-auto-rows: 130px;
  grid-gap: 20px;
}

.gallery__item {
  height: 100%;
  background-color: #D8D8D8;
}

.gallery__item:hover,
.gallery__item:focus {
  background-color: #A4A4A4;
}

<!-- center the h1 text -->
#content h1 {
  text-align: center;
  margin-left: auto;
  margin-right: auto;
  max-width: 900px; /* optional: limit line length */
  padding: 0 16px;  /* optional: horizontal padding on small screens */
}
.join-button {
        background-color: #4CAF50; /* Green */
        color: white;
        padding: 15px 32px;
        text-align: center;
        text-decoration: none;
        display: inline-block;
        font-size: 16px;
        margin: 4px 2px;
        cursor: pointer;
        border: none;
    }

@media (max-width:640px) {
    .container {
        display: block; /* Stack panes vertically on mobile */
    }
    
    .pane {
        width: 100%; /* Full width for mobile panes */
    }
  
  .gallery {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    justify-items: center;
    gap: 12px;
  }

  .gallery__item {
    width: 120px;
    height: 120px;
  }

  .gallery__item.qr {
    grid-column: 1 / -1; /* make QR occupy full row so it's centered */
    justify-self: center;
    width: 140px;
    height: 140px;
  }

  .gallery__item img { width:100%; height:100%; object-fit:cover; display:block; }
}