Open menu effect | Pure CSS

index.haml

%label
  %input{"type"=> "checkbox"} 
  %span.menu
    %span.hamburger
  %ul 
    %li
      %a{"href"=>"#"} Home
    %li
      %a{"href"=>"#"} About
    %li
      %a{"href"=>"#"} Work
  
%h1 Click the hamburger icon to view the effect

open-menu-effect-pure-css.markdown

Open menu effect | Pure CSS

Uses checkbox to open the menu

A Pen by Håvard Brynjulfsen on CodePen.

License.

style.scss

@import url('https://fonts.googleapis.com/css?family=Cutive+Mono');

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

html {
  font-size: 18px;
}

body {
  font-family: "Cutive Mono", serif;
  font-size: 1.2em;
  line-height: 1.6;
  background: #CCC;
  overflow-x: hidden;
}

label {
  .menu {
    position: absolute;
    right: -100px;
    top: -100px;
    z-index: 100;
    width: 200px;
    height: 200px;
    background: #FFF;
    border-radius: 50% 50% 50% 50%;
    transition: .5s ease-in-out;
    box-shadow: 0 0 0 0 #FFF, 0 0 0 0 #FFF;
    cursor: pointer;
  }
  .hamburger {
    position: absolute;
    top: 135px;
    left: 50px;
    width: 30px;
    height: 2px;
    background: #000;
    display: block;
    transform-origin: center;
    transition: .5s ease-in-out;
    &:after,
    &:before {
      transition: .5s ease-in-out;
      content: "";
      position: absolute;
      display: block;
      width: 100%;
      height: 100%;
      background: #000;
    }
    &:before {
      top: -10px;
    } 
    &:after {
      bottom: -10px;
    }
  }
  input {
    display: none;
  }
  input:checked + .menu {
    box-shadow: 0 0 0 100vw #FFF, 0 0 0 100vh #FFF;
    border-radius: 0;
    .hamburger {
      transform: rotate(45deg);
      &:after {
        transform: rotate(90deg);
        bottom: 0;
      }
      &:before {
        transform: rotate(90deg);
        top: 0;
      }
    }
  }
  
  input:checked + .menu + ul {
    opacity: 1;
  }
  
  ul {
    z-index: 200;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    opacity: 0;
    transition: .25s 0s ease-in-out;
  }
  
  a {
    margin-bottom: 1em;
    display: block;
    color: #000;
    text-decoration: none;
  }
}

h1 {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
  width: 80%;
  text-align: center;
}