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

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

.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  max-width: $sidebar-width;
  height: 100%;
  z-index: 50;

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

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

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

    /* line hover effect */
    a {
      position: relative;
      color: $base-color;

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

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

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

  > .inner {
    width: 100%;
    height: 100%;
    padding: 1.5em;
    background-color: $sidebar-background-color;
    overflow-x: hidden;
    box-shadow: inset -1em 0 5em 0 rgba(0, 0, 0, 0.125);

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

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

    a {
      display: block;
    }

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

    li {
      margin-bottom: 1.5rem;
    }
  }

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

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

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

.sidebar-toggle-wrapper {
  position: fixed;
  top: 0.675rem;
  right: 0;
  cursor: pointer;
  z-index: 10000;

  .toggle {
    display: -ms-flexbox;
    display: flex;
    -ms-flex-align: center;
    align-items: center;
    color: inherit;
    text-decoration: none;
  }
}

.sidebar-toggle-label {
  -ms-flex-order: 2;
  order: 2;
  margin-left: 0.5rem;
  font-weight: bold;
}