.apos-modal
{
  @apos-tabs-width: 220px;

  .apos-schema-tabs
  {
    float: left;
    height: 100%;
    width: @apos-tabs-width;
    background-color: @apos-light;
  }

  .apos-schema--with-tabs .apos-schema-tabs {}

  .apos-schema-tab
  {
    padding: @apos-padding-2;
    border-bottom: 1px solid @apos-dark;
    font-size: 16px;
    cursor: pointer;
    &.apos-active
    {
      background-color: @apos-white;
      cursor: default;
    }
  }

  .apos-schema-group
  {
    display: none;
    float: left;
    width: calc(~"100% - " @apos-tabs-width);
    height: 100%;
    overflow-y: scroll;
    .apos-scrollbar;
  }

  .apos-schema-group.apos-active
  {
    display: block;
  }

  .apos-schema-group-inner
  {
    width: 100%;
    max-width: 540px;
    min-height: 100%;
    padding: @apos-padding-2;
    background-color: @apos-white;
  }
}

.apos-modal
{
  @apos-tabs-width: 220px;

  .apos-schema-tabs
  {
    position: fixed;
    float: left;
    height: 100%;
    width: @apos-tabs-width;
    background-color: @apos-light;
    // If tab number exceeds viewport allow scroll
    overflow: scroll;
  }

  .apos-schema--with-tabs .apos-schema-tabs {}

  .apos-schema-tab
  {
    padding: @apos-padding-2;
    border-bottom: 1px solid @apos-dark;
    font-size: 16px;
    cursor: pointer;
    &.apos-active
    {
      background-color: @apos-white;
      cursor: default;
    }
  }

  .apos-schema-group
  {
    display: none;
    float: left;
    width: calc(~"100% - " @apos-tabs-width);
    height: 100%;
    overflow-y: scroll;
    .apos-scrollbar;
  }

  .apos-schema-group.apos-active
  {
    display: block;
  }

  .apos-schema-group-inner
  {
    width: 100%;
    max-width: 540px;
    min-height: 100%;
    margin-left: @apos-tabs-width;
    padding: @apos-padding-2;
    background-color: @apos-white;
  }
}

Add fixed position to modal tabs
Add fixed position to modal tabs
