<div class="wrapper">
  <input type="checkbox" id="menuToggler" class="input-toggler" value="1" autofocus="true"/>
  <label for="menuToggler" id="menuTogglerLabel" class="menu-toggler" role="button" aria-pressed="false" aria-expanded="false" aria-label="Navigation button">
    <span class="menu-toggler__line"></span>
    <span class="menu-toggler__line"></span>
    <span class="menu-toggler__line"></span>
  </label>
  <nav id="sidebar" class="sidebar" role="navigation" aria-labelledby="menuTogglerLabel" aria-hidden="true">
    <ul id="menubar" class="menu" role="menubar" aria-orientation="vertical">
      <li class="menu__item" role"none"><a class="menu__link" href="#" role="menuitem" tabindex="-1">Home</a></li>
      <li class="menu__item" role"none"><a class="menu__link" href="#" role="menuitem" tabindex="-1">Blog</a></li>
      <li class="menu__item" role"none"><a class="menu__link" href="#" role="menuitem" tabindex="-1">Portfolio</a></li>
      <li class="menu__item" role"none"><a class="menu__link" href="#" role="menuitem" tabindex="-1">About</a></li>
      <li class="menu__item" role"none"><a class="menu__link" href="#" role="menuitem" tabindex="-1">Contact</a></li>
    </ul>
  </nav>
  <main class="content">
    <h1>CSS sidebar toggle</h1>
    <p>Pure CSS solution for hiding and showing sidebar.</p>
  </main>
</div>
<a class="sb-link" href="//silvestar.codes/articles/css-sidebar-toggle/">silvestar.codes</a>

@mixin fluid-type($properties, $min-vw, $max-vw, $min-value, $max-value) {
    @each $property in $properties {
        #{$property}: $min-value;
    }

    @media screen and (min-width: $min-vw) {
        @each $property in $properties {
            #{$property}: calc(#{$min-value} + #{strip-unit($max-value - $min-value)} * (100vw - #{$min-vw}) / #{strip-unit($max-vw - $min-vw)});
        }
    }

    @media screen and (min-width: $max-vw) {
        @each $property in $properties {
            #{$property}: $max-value;
        }
    }
}

@function strip-unit($value) {
    @return $value / ($value * 0 + 1);
}

@function em($pixels, $context: $default-font-size) {
    @return #{$pixels/$context}em;
}

// variables
:root {
  --sidebar-width: 100%;
  --toggler-size: 30px;
  --toggler-line-number: 3;
  --toggler-line-size: calc(var(--toggler-size) / (var(--toggler-line-number) + var(--toggler-line-number) - 1));
  --toggler-offset-left: 10px;
  --toggler-offset-top: 10px;
  --toggler-color: Tomato;
  --toggler-color-hover: Wheat;
}

// same as var(--toggler-line-number)
$total: 3;

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

// styling
html {
  font-family: -apple-system, BlinkMacSystemFont,
"Segoe UI", "Roboto", "Oxygen",
"Ubuntu", "Cantarell", "Fira Sans",
"Droid Sans", "Helvetica Neue", sans-serif;
  @include fluid-type(font-size, 20em, 75em, .8rem, 1.2rem);
}

.wrapper {
  min-width: 100vw;
  background: AliceBlue;
  display: flex;
}

.sidebar,
.content {
  transition: all .25s ease-out;
}

.sidebar {
  width: var(--sidebar-width);
  transform: translateX(calc(var(--sidebar-width) * -1));
  background: linear-gradient(to bottom right, Tomato, Wheat);
  display: flex;
  justify-content: center;
  align-items: center;
  position: absolute;
  top: 0;
  height: 100vh;
  opacity: .5;
}

.content {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
}

.menu {
  list-style-type: none;
}

.menu__link {
  color: white;
  font-weight: 100;
  text-decoration: none;
  font-size: 10vmin;
  line-height: 15vmin;
  transition: all .25s ease-out;
  
  &:hover,
  &:focus,
  &:active {
    color: Gold;
  }
}

.menu-toggler {
  border-radius: calc(var(--toggler-line-size) / 2);
  display: block;
  width: var(--toggler-size);
  height: var(--toggler-size);
  position: fixed;
  top: var(--toggler-offset-top);
  left: var(--toggler-offset-left);
  cursor: pointer;
  z-index: 1;
}

.menu-toggler__line {
  height: var(--toggler-line-size);
  background: var(--toggler-color);
  position: absolute;
  border-radius: calc(var(--toggler-line-size) / 2);
  left: 0;
  right: 0;
  transition: all .25s ease-out;
  
  $num: 1;
  
  @while $num <= $total {
    &:nth-child(#{$num}) {
      top: calc(var(--toggler-line-size) * #{$num} + (var(--toggler-line-size) * (#{$num} - 2)));
    }
    
    $num: $num + 1;
  }    
}

.input-toggler {
  position: absolute;
  left: -100%;
  
  &:focus ~ .menu-toggler {
    outline: 1px dotted;
  }
  
  &:checked ~ .menu-toggler {    
    .menu-toggler__line:not(:first-child):not(:last-child) {
      opacity: 0;
    }
    
    .menu-toggler__line:first-child,
    .menu-toggler__line:last-child {
      background-color: var(--toggler-color-hover);
    }      
    
    .menu-toggler__line:first-child {
      transform: translateY(calc(var(--toggler-line-size) * (var(--toggler-line-number) - 1))) rotate(45deg);
    }
    
    .menu-toggler__line:last-child {
      transform: translateY(calc(-1 * var(--toggler-line-size) * (var(--toggler-line-number) - 1))) rotate(-45deg);
    }
  }
  
  &:checked ~ .sidebar {
    transform: translateX(0);
    opacity: .98;
  }
}

// sig
.wrapper {
  height: calc(100vh - 50px);
}

.sb-link {
  display: flex;
  height: 50px;
  align-content: center;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  color: #bb5555;
  transition: background .3s;
}

.sb-link:hover,
.sb-link:focus,
.sb-link:active {
  background: #f7f7f7;
}

let menuToggler = document.getElementById('menuToggler')
let menuTogglerLabel = document.getElementById('menuTogglerLabel');
let sidebar = document.getElementById('sidebar');
let menuItems = document.getElementsByClassName('menu__link');

menuToggler.addEventListener('change', function() {
  if(menuToggler.checked) {
    menuTogglerLabel.setAttribute('aria-pressed', 'true');
    sidebar.setAttribute('aria-hidden', 'false');    
  } else {
    menuTogglerLabel.setAttribute('aria-pressed', 'false');
    sidebar.setAttribute('aria-hidden', 'true');
  }
  
  for(let menuItem of menuItems) {
    if(menuToggler.checked) {
      menuItem.setAttribute('tabindex', '0');
    } else {
      menuItem.setAttribute('tabindex', '-1');
    }
  }  
});