datat.fi/_sass/basically-basic/_sidebar.scss

/* ==========================================================================
   Sidebar
   ========================================================================== */

#sidebar {
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
  pointer-events: none;
  z-index: 150;

  /* page overlay dimmer */
  &:after {
    content: '';
    display: block;
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: rgba($base-color, 0.5);
    opacity: 0;
    will-change: opacity;
    pointer-events: none;
    transition: opacity 0.3s cubic-bezier(0, 0, 0.3, 1);
  }

  /* line hover effect */
  li {

    a {
      position: relative;
      color: $base-color;

      &:before {
        content: '';
        display: block;
        position: absolute;
        top: 50%;
        left: -3rem;
        height: 1px;
        width: 0;
        background-color: $base-color;
        transition: width 0.3s cubic-bezier(0, 0, 0.3, 1);
      }

      &:hover {
        color: $accent-color;
      }

      &:hover:before {
        width: 2.5rem;
      }
    }
  }

  &.is--visible {
    -ms-transform: translateX(0);
        transform: translateX(0);

    &:after {
      opacity: 1;
      pointer-events: auto;
    }

    > .inner {
      box-shadow: 0 1em 5em 0 rgba(0, 0, 0, 0.125);
      -ms-transform: none;
          transform: none;
    }
  }

  &.is--animatable > .inner {
    transition: all 130ms ease-in;
  }

  &.is--visible.is--animatable > .inner {
    transition: all 330ms ease-out;
  }

  > .inner {
    position: relative;
    padding: 1.5em;
    width: 100%;
    max-width: $sidebar-width;
    height: 100%;
    overflow-x: hidden;
    background-color: $sidebar-background-color;
    box-shadow: none;
    -ms-transform: translateX(-1 * $sidebar-width);
        transform: translateX(-1 * $sidebar-width);
    will-change: transform;
    z-index: 160;
    pointer-events: auto;

    @include breakpoint($medium) {
      padding: 3rem;
    }

    @include breakpoint($large) {
      -ms-transform: translateX(-1.5 * $sidebar-width);
          transform: translateX(-1.5 * $sidebar-width);
      max-width: (1.5 * $sidebar-width);
    }
  }

  .menu {
    position: relative;
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    @include fluid-type($min-vw, $max-vw, 24px, 48px);
    font-weight: bold;
    line-height: 1;

    a {
      display: block;
    }

    /* divider line */
    &:after {
      content: '';
      position: absolute;
      bottom: 0;
      width: 1.5em;
      height: 1px;
      background-color: $base-color;
    }

    li {
      margin-bottom: 1.5rem;
    }
  }


  li {
    -ms-transform: translateX(-1rem);
        transform: translateX(-1rem);
    opacity: 0;
    transition: all 0.5s;

    &.is--moved {
      opacity: 1;
      -ms-transform: translateX(0);
          transform: translateX(0);
    }
  }

  .contact-list {
    margin-top: 0.5rem;
    padding-top: 0.5rem;
    @include fluid-type($min-vw, $max-vw, 18px, 24px);

    li:not(:last-child) {
      margin-bottom: 0.5rem;
    }

    a {
      display: block;
      color: $base-color;
      text-decoration: none;
    }
  }
}

#sidebar-toggle {
  position: fixed;
  top: 0;
  right: 0;
  cursor: pointer;
  z-index: 10000;
}