discourse/app/assets/stylesheets/common/base/sidebar.scss

:root {
  --d-sidebar-width: #{$d-sidebar-width};
  @include breakpoint(large) {
    --d-sidebar-width: #{$d-sidebar-narrow-width};
  }
  --d-sidebar-animation-time: 0.25s;
  --d-sidebar-animation-ease: ease-in-out;
  // 1.25rem gets text left-aligned with the hamburger icon
  --d-sidebar-row-horizontal-padding: 1.25rem;
  // ems so height is variable along with font size
  --d-sidebar-row-height: 2.15em;
}

.sidebar-row {
  box-sizing: border-box;
  height: var(--d-sidebar-row-height);
  padding: 0 var(--d-sidebar-row-horizontal-padding);
  align-items: center;
}

.sidebar-wrapper {
  display: flex;
  --d-sidebar-highlight-color: var(--primary-low);
  background-color: var(--primary-very-low);
  grid-area: sidebar;
  position: sticky;
  top: var(--header-offset);

  @include unselectable;

  // 1dvh with fallback for old browsers
  --1dvh: 1vh;
  @supports (height: 1dvh) {
    --1dvh: 1dvh;
  }

  height: calc(
    var(--composer-vh, var(--1dvh)) * 100 - var(--header-offset, 0px)
  );

  align-self: start;
  overflow-y: auto;

  .sidebar-container {
    display: flex;
    flex-direction: column;
    box-sizing: border-box;
    height: 100%;
    width: 100%;
    padding: 0;
    overflow-x: hidden;
    // allows sidebar to scroll to the bottom when the composer is open
    height: calc(100% - var(--composer-height, 0px));
  }

  .sidebar-sections {
    display: flex;
    flex-direction: column;
    box-sizing: border-box;
    flex: 1;
    padding: 1.35em 0 1em;
    overflow-x: hidden;
    overflow-y: overlay;

    // custom scrollbar styling
    --scrollbarBg: transparent;
    --scrollbarThumbBg: var(--primary-low);
    --scrollbarWidth: 0.5em;

    scrollbar-color: transparent var(--scrollbarBg);
    transition: scrollbar-color 0.25s ease-in-out;
    transition-delay: 0.5s;

    &::-webkit-scrollbar {
      width: var(--scrollbarWidth);
    }

    &::-webkit-scrollbar-thumb {
      background-color: transparent;
      border-radius: calc(var(--scrollbarWidth) / 2);
    }

    &::-webkit-scrollbar-track {
      background-color: transparent;
    }

    &:hover {
      scrollbar-color: var(--scrollbarThumbBg) var(--scrollbarBg);

      &::-webkit-scrollbar-thumb {
        background-color: var(--scrollbarThumbBg);
      }

      transition-delay: 0s;
    }
  }
  .sidebar-footer-wrapper {
    .btn-flat.add-section {
      padding: 0.25em 0.4em;
      &:hover {
        background: var(--d-sidebar-highlight-color);
        svg {
          color: var(--primary-medium);
        }
      }
    }
  }
}

.sidebar-section-form-modal {
  .modal-inner-container {
    width: var(--modal-max-width);
  }
  form {
    margin-bottom: 0;
  }
  .input-group input {
    width: 100%;
  }
  input.warning {
    border: 1px solid var(--danger);
  }
  .row-wrapper {
    display: grid;
    grid-template-columns: auto auto auto 2em;
    gap: 1em;
    margin-top: 1em;
  }
  .delete-link {
    height: 1em;
    align-self: end;
    margin-bottom: 0.75em;
    margin-right: 1em;
  }
  .btn-flat.add-link {
    margin-top: 1em;
    margin-left: -0.65em;
    &:active,
    &:focus {
      background: none;
    }
    svg {
      color: var(--tertiary);
      width: 0.75em;
      height: 0.75em;
    }
    &:hover svg {
      color: var(--tertiary-hover);
    }
  }
  .modal-footer {
    display: flex;
    justify-content: space-between;

    .delete {
      margin-right: 0;
    }
  }
}