offscreen-menu.css

.navigation {
  width: 100%;
  height: 100%;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 0;
  list-style: none;
  background: #111;
}

.nav-item {
  width: 200px;
  border-top: 1px solid #111;
  border-bottom: 1px solid #000;
}

.nav-item a {
  display: block;
  padding: 1em;
  background: linear-gradient(135deg, rgba(0,0,0,0) 0%,rgba(0,0,0,0.65) 100%);
  color: white;
  font-size: 1.2em;
  text-decoration: none;
  transition: color 0.2s, background 0.5s;
}

.nav-item a:hover {
  color: #c74438;
  background: linear-gradient(135deg, rgba(0,0,0,0) 0%,rgba(75,20,20,0.65) 100%);
}

.site-wrap {
  min-height: 100%;
  min-width: 100%;
  background-color: white; 
  position: relative;
  top: 0;
  bottom: 100%;
  left: 0;
  z-index: 1;
  padding: 4em;
  background-image: linear-gradient(135deg, rgb(254,255,255) 0%,rgb(221,241,249) 35%,rgb(160,216,239) 100%);
  background-size: 200%;
}

.nav-trigger {
  position: absolute;
  clip: rect(0, 0, 0, 0);
}

label[for="nav-trigger"] {
  position: fixed;
  left: 15px; top: 15px;
  z-index: 2;
  height: 30px;
  width: 30px;
  cursor: pointer;
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' version='1.1' x='0px' y='0px' width='30px' height='30px' viewBox='0 0 30 30' enable-background='new 0 0 30 30' xml:space='preserve'><rect width='30' height='6'/><rect y='24' width='30' height='6'/><rect y='12' width='30' height='6'/></svg>");
  background-size: contain;
}

.nav-trigger + label, .site-wrap {
  transition: left 0.2s;
}

.nav-trigger:checked + label {
  left: 215px;
}

.nav-trigger:checked ~ .site-wrap {
  left: 200px;
  box-shadow: 0 0 5px 5px rgba(0,0,0,0.5);
}

body {
  overflow-x: hidden;
}