Easier is to just mention the owner @Pollux (ping). He's a mod here, so very likely to see it anyhow.

Add this to your custom styles

@media @desktop-up {
  .sideNavOffset {
    margin-left: 0;
  }

  .sideNav {
    margin-right: 0;
    margin-left: 50px;

    &.TagsPage-nav {
      margin-left: 0;
    }
  }

  .sideNavContainer {
    flex-direction: row-reverse;
  }
}

    LYDR3X

    I am the founder and maintainer of Moccato and I created this style. The style of my forum is a large set of rules working together. It was a lot of customizing necessary to achieve this look.

    The way I moved the sidebar to the right is certainly not the only way of doing it, probably nxta's approach is a more elegant one. But I can show you how I did it (not the whole thing, just the first steps).

    Start with moving the sideNav bar to the right:

    .sideNavContainer {
    display: block;
}
.IndexPage-nav:not(.TagsPage-nav),
.DiscussionPage-nav,
.UserPage-nav {
    float: right;
    width: 8.5vw;
}
.IndexPage-nav:not(.TagsPage-nav) > ul > li,
.DiscussionPage-nav > ul > li,
.UserPage-nav > ul > li {
    margin-left: -60px;
}

    Note: I have disabled the display: flex of the .sideNavContainer replacing it with old school block. Furthermore I adressed only certain types of sideNav: .IndexPage-nav (except .TagsPage-nav),
    .DiscussionPage-nav and .UserPage-nav. The width of the sideNav is a combination of fixed values (-60px) and relative values (8.5vw).

    Then provide the div with the results space on the right side, again a combined effect of padding (fixed value) and margin (relative value):

    .sideNavOffset {
    padding-right: 100px;
    margin-right: 12vw;
}

    Et voilà, doesn't look too bad... but it's just a start.

          6 months later

          Pollux Can you share the whole style of your forum? It's really wonderful, I like it too much.

              9 days later

              Gatsu Can you share the whole style of your forum? It's really wonderful, I like it too much.

              Sorry for my late reply.

              My style is not particularly documented, nor is it organized according to the different effects, and it depends on private extensions that I have cobbled together for our very special needs. In the end, it will be much easier to re-create this style than to break down my specific CSS rules.

              If you are interested in some specific techniques I will be glad to help.

                2 months later

                or don't change the flex setup at all and just use this:

                .sideNav{
  margin-left: 50px;
  order: 1;
}