tabler/core/scss/layout/_navbar.scss

@mixin navbar-vertical-nav {
  .navbar-collapse {
    flex-direction: column;

    [class^="container"] {
      flex-direction: column;
      align-items: stretch;
      padding: 0;
    }

    .navbar-nav {
      margin-left: 0;
      margin-right: 0;

      .nav-link {
        padding: 0.5rem calc(#{$container-padding-x} / 2);
        justify-content: flex-start;
      }
    }

    .dropdown-menu-columns {
      flex-direction: column;
    }

    .dropdown-menu {
      padding: 0;
      background: transparent;
      position: static;
      color: inherit;
      box-shadow: none;
      border: none;
      min-width: 0;
      margin: 0;

      .dropdown-item {
        min-width: 0;
        display: flex;
        width: auto;
        padding-left: add(calc(#{$container-padding-x} / 2), 1.75rem);
        color: inherit;

        &.disabled {
          color: var(--#{$prefix}disabled-color);
          pointer-events: none;
          background-color: transparent;
        }

        &.active,
        &:active {
          background: var(--#{$prefix}navbar-active-bg);
        }
      }

      .dropdown-menu .dropdown-item {
        padding-left: add(calc(#{$container-padding-x} / 2), 3.25rem);
      }

      .dropdown-menu .dropdown-menu .dropdown-item {
        padding-left: add(calc(#{$container-padding-x} / 2), 4.75rem);
      }
    }

    .dropdown-toggle:after {
      margin-left: auto;
    }

    .nav-item.active:after {
      border-bottom-width: 0;
      border-left-width: 3px;
      right: auto;
      top: 0;
      bottom: 0;
    }
  }
}

/**
Navbar
 */
.navbar {
  --#{$prefix}navbar-bg: var(--#{$prefix}bg-surface);
  --#{$prefix}navbar-border-width: #{$navbar-border-width};
  --#{$prefix}navbar-active-border-color: #{$navbar-active-border-color};
  --#{$prefix}navbar-active-bg: #{$navbar-light-active-bg};
  --#{$prefix}navbar-border-color: #{$navbar-border-color};
  --#{$prefix}navbar-hover-color: #{$navbar-hover-color};
  align-items: stretch;
  min-height: $navbar-height;
  box-shadow: inset 0 calc(-1 * var(--#{$prefix}navbar-border-width)) 0 0 var(--#{$prefix}navbar-border-color);
  background: var(--#{$prefix}navbar-bg);
  color: var(--#{$prefix}navbar-color);

  .navbar-collapse & {
    flex-grow: 1;
  }

  &.collapsing {
    min-height: 0;
  }

  .dropdown-menu {
    position: absolute;
    z-index: $zindex-fixed;
  }

  .navbar-nav {
    min-height: subtract($navbar-height, 2 * $navbar-padding-y);

    .nav-link {
      position: relative;
      min-width: 2.5rem;
      min-height: 2.5rem;
      justify-content: center;
      border-radius: var(--#{$prefix}border-radius);

      .badge {
        position: absolute;
        top: 0.375rem;
        right: 0.375rem;
        transform: translate(50%, -50%);
      }
    }
  }
}

.navbar-expand {
  @each $breakpoint in map-keys($grid-breakpoints) {
    $next: breakpoint-next($breakpoint, $grid-breakpoints);
    $infix: breakpoint-infix($next, $grid-breakpoints);

    &#{$infix} {
      @include media-breakpoint-down(breakpoint-next($breakpoint)) {
        @include navbar-vertical-nav;
      }

      @include media-breakpoint-up($next) {
        .navbar-collapse {
          width: auto;
          flex: 1 1 auto;
        }

        .nav-item.active {
          position: relative;

          .nav-link {
            color: var(--#{$prefix}navbar-active-color);
          }

          &:after {
            content: "";
            position: absolute;
            left: 0;
            right: 0;
            bottom: -0.25rem;
            border: 0 var(--#{$prefix}border-style) var(--#{$prefix}navbar-active-border-color);
            border-bottom-width: 2px;
          }
        }

        &.navbar-vertical {
          box-shadow: inset calc(-1 * var(--#{$prefix}navbar-border-width)) 0 0 0 var(--#{$prefix}navbar-border-color);

          &.navbar-right,
          &.navbar-end {
            box-shadow: inset calc(1 * var(--#{$prefix}navbar-border-width)) 0 0 0 var(--#{$prefix}navbar-border-color);
          }
        }

        &.navbar-vertical {
          ~ .navbar,
          ~ .page-wrapper {
            margin-left: $sidebar-width;
          }
        }

        &.navbar-vertical.navbar-right,
        &.navbar-vertical.navbar-end {
          ~ .navbar,
          ~ .page-wrapper {
            margin-left: 0;
            margin-right: $sidebar-width;
          }
        }
      }
    }
  }
}

/**
Navbar brand
 */
.navbar-brand {
  display: inline-flex;
  align-items: center;
  font-weight: $navbar-brand-font-weight;
  margin: 0;
  line-height: 1;
  gap: $spacer-2;
}

.navbar-brand-image {
  height: $navbar-brand-image-height;
  width: auto;
}

/**
Navbar toggler
 */
.navbar-toggler {
  border: 0;
  width: $navbar-brand-image-height;
  height: $navbar-brand-image-height;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
}

.navbar-toggler-icon {
  height: 2px;
  width: 1.25em;
  background: currentColor;
  border-radius: 10px;
  position: relative;
  @include transition(
    top $navbar-toggler-animation-time $navbar-toggler-animation-time,
    bottom $navbar-toggler-animation-time $navbar-toggler-animation-time,
    transform $navbar-toggler-animation-time,
    opacity 0s $navbar-toggler-animation-time
  );
  
  &:before,
  &:after {
    content: "";
    display: block;
    height: inherit;
    width: inherit;
    border-radius: inherit;
    background: inherit;
    position: absolute;
    left: 0;
    @include transition(inherit);
  }

  &:before {
    top: -0.45em;
  }

  &:after {
    bottom: -0.45em;
  }

  .navbar-toggler[aria-expanded="true"] & {
    transform: rotate(45deg);
    @include transition(top $transition-time, bottom $transition-time, transform $transition-time $transition-time, opacity 0s $transition-time);

    &:before {
      top: 0;
      transform: rotate(-90deg);
    }

    &:after {
      bottom: 0;
      opacity: 0;
    }
  }
}

/**
Navbar transparent
 */
.navbar-transparent {
  --#{$prefix}navbar-border-color: transparent !important;
  background: transparent !important;
}

/**
Navbar nav
 */
.navbar-nav {
  --#{$prefix}nav-link-hover-bg: #{color-transparent(var(--#{$prefix}nav-link-color), 0.04)};
  margin: 0;
  padding: 0;
  align-items: stretch;

  .nav-item {
    display: flex;
    flex-direction: column;
    justify-content: center;
  }
}

/**
Navbar side
 */
.navbar-side {
  margin: 0;
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: space-around;
}

/**
Navbar vertical
 */
@if $enable-navbar-vertical {
  .navbar-vertical {
    &.navbar-expand {
      @each $breakpoint in map-keys($grid-breakpoints) {
        $next: breakpoint-next($breakpoint, $grid-breakpoints);
        $infix: breakpoint-infix($next, $grid-breakpoints);

        &#{$infix} {
          @include media-breakpoint-up($next) {
            width: $sidebar-width;
            position: fixed;
            top: 0;
            left: 0;
            bottom: 0;
            z-index: $zindex-fixed;
            align-items: flex-start;
            overflow-y: scroll;
            padding: 0;
            @include transition(transform $transition-time);

            &.navbar-right,
            &.navbar-end {
              left: auto;
              right: 0;
            }

            .navbar-brand {
              padding: (($navbar-height - $navbar-brand-image-height) * 0.5) 0;
              justify-content: center;
            }

            .navbar-collapse {
              align-items: stretch;
            }

            .navbar-nav {
              flex-direction: column;
              flex-grow: 1;
              min-height: auto;

              .nav-link {
                padding-top: 0.5rem;
                padding-bottom: 0.5rem;
              }
            }

            > [class^="container"] {
              flex-direction: column;
              align-items: stretch;
              min-height: 100%;
              justify-content: flex-start;
              padding: 0;
            }

            ~ .page {
              padding-left: $sidebar-width;

              [class^="container"] {
                padding-left: 1.5rem;
                padding-right: 1.5rem;
              }
            }

            &.navbar-right ~ .page,
            &.navbar-end ~ .page {
              padding-left: 0;
              padding-right: $sidebar-width;
            }

            @include navbar-vertical-nav;
          }
        }
      }
    }
  }
}

.navbar-overlap {
  &:after {
    content: "";
    height: $navbar-overlap-height;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: inherit;
    z-index: -1;
    box-shadow: inherit;
  }
}