HTML+Sass implements HambergurMenu (hamburger menu)

/*Set color and max-width*/
$primary-color: rgba(13,110,139,.75);
$overlay-color: rgba(24,39,51,.85);
$max-width: 980px;

/*Set the text color. If the background color is light, set it to black, otherwise set it to white*/
@function set-text-color($color){
  @if(lightness($color)>70){
    @return #333;
  }@else{
    @return #fff;
  }
}

/*Mixer, set background color and text color*/
@mixin set-background($color){
  background-color: $color;
  color: set-text-color($color);
}

@import '_config';
*{
  margin: 0;
  padding: 0;
}

.container{
  max-width: $max-width;
  margin: 0 auto;
}

/*Set the background color for showcase, add a background image using pseudo-class, and set the z-index of the background image to -1 (so that the image will be displayed inside);
Then in order to make the text appear in the middle, flex layout is used*/
.showcase{
  position: relative;
  height: 100vh;
  background-color: $primary-color;
  &:before{
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: url('../img/pexels-photo-533923.jpeg') no-repeat center center / cover;
    z-index: -1;
  }
  &-inner{
    display: flex;
    height: 100%;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    color: #fff;
    font-weight: 100;
    h1{
      font-size: 4rem;
      padding: 1.2rem 0;
    }
    p{
      white-space: pre-wrap;
      font-size: 1.6rem;
      padding: 0.85rem 0;
    }
    .btn{
      padding: .65rem 1rem;
        /*Use the mixer to set the background color and text color*/
      @include set-background(lighten($primary-color,30%));
      border: none;
      border: 1px solid $primary-color;
      border-radius: 5px;
      text-decoration: none;
      outline: none;
      transition: all .2s ease .1s;
        /*When the button is hovered, use CSS3 scale to set a zoom effect*/
      &:hover{
        @include set-background(lighten($overlay-color,30%));
        border-color: lighten($overlay-color, 25%);
        transform: scale(.98);
      }
    }
  }
}

/*Principle: Change the style by clicking on the checkbox (set the checkbox transparency to 0 and the z-index to a higher level). When you click, a menu will appear. Click again and the menu will disappear*/
/*Set menu-wrap to fixed so that the showcase will fill the entire screen; also set the opacity of the checkbox to 0;
Also note that you need to set the z-index of the checkbox to 2, because the z-index of the hamburger is set to 1, otherwise the click will not work*/
.menu-wrap{
  position: fixed;
  left: 0;
  top: 0;
  z-index: 1;
  .toggle{
    position: absolute;
    left: 0;
    top: 0;
    width: 50px;
    height: 50px;
    opacity: 0;
    z-index: 2;
    cursor: pointer;
      /*When the checkbox is checked, set the rotation effect of the div and pseudo class in the hamburger*/
    &:checked ~ .hamburger>div{
      transform: rotate(135deg);
        /*The pseudo class is actually rotated 225 degrees, so top needs to be set to 0, otherwise the length of the ❌ will be inconsistent*/
      &:before,&:after{
        transform: rotate(90deg);
        top: 0;
      }
    }

      /*When the checkbox is selected and hovered, a rotation effect will also be set*/
    &:checked:hover ~ .hamburger>div{
      transform: rotate(235deg);
    }
    &:checked ~ .menu{
      visibility: visible;
      >div{
        transform: scale(1);
        >div{
          opacity: 1;
        }
      }
    }
  }
    
  .hamburger{
    position: absolute;
    left: 0;
    top: 0;
    width: 60px;
    height: 60px;
    padding: 1rem;
    background-color: $primary-color;
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    z-index: 1;
      /*The div itself generates a horizontal line in the middle, then sets the positioning to relative, and then sets its pseudo-class to absolute.
      Offset relative to div*/
    >div{
      position: relative;
      left: 0;
      top: 0;
      width: 100%;
      height: 2px;
      background-color: #fff;
      transition: all .7s ease;
        /*Use pseudo-class to generate the first and third horizontal lines*/
      &:before,
      &:after{
        content: '';
        position: absolute;
        left: 0;
        top: -10px;
        width: 100%;
        height: 2px;
        background-color: inherit;
      }
      &:after{
        top: 10px;
      }
    }
  }

    /*Set the style of the selected menu*/
    /*Set the menu to fixed, with a width and height of 100%, and then set the display to flex, otherwise the menu will not appear in the middle*/
  .menu{
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    visibility: hidden; /*Set the menu to invisible, and then set it to visible when the checkbox is selected*/
    transition: all .75s ease;
    >div{
      @include set-background($overlay-color);
      width: 200vw;
      height: 200vh;
      overflow: hidden;
      border-radius: 50%;
      display: flex;
      justify-content: center;
      align-items: center;
      text-align: center;
      transform: scale(0);
      transition: all .4s ease;
      >div{
        max-width: 90vw;
        max-height: 90vh;
        opacity: 0;
        transition: all .4s ease;
        >ul>li{
          list-style: none;
          font-size: 2rem;
          padding: .85rem 0;
          text-transform:uppercase;
          transform: skew(-5deg,-5deg) rotate(5deg);/*Set text tilt*/
          a{
            color: inherit;
            text-decoration: none;
            transition: color .4s ease;
          }
        }
      }
    }
  }
}