Keeps the sidebar ribbon out of sight and only shows it upon hover. [Not tested on Obsidian 1.0+]

obsidian-show-ribbon-on-hover.css

/*HIDE RIBBON WHEN SIDEBAR IS COLLAPSED*/
.side-dock-ribbon.mod-left.is-collapsed .side-dock-ribbon-action {
    opacity: 0;
    transition: opacity .3s;  
}
.side-dock-ribbon.mod-left.is-collapsed:hover .side-dock-actions:hover .side-dock-ribbon-action,
.side-dock-ribbon.mod-left.is-collapsed:hover .side-dock-settings:hover .side-dock-ribbon-action {
    opacity: 1;
}


/*HIDE RIBBON WHEN SIDEBAR IS EXPANDED*/
.side-dock-ribbon.mod-left:not(.is-collapsed) .side-dock-ribbon-action,
.side-dock-ribbon.mod-left:not(.is-collapsed) .workspace-ribbon-collapse-btn svg {
    opacity: 0;
}
.side-dock-ribbon.mod-left.is-collapsed .workspace-ribbon-collapse-btn:not(hover) + .side-dock-actions:hover .side-dock-ribbon-action,
.side-dock-ribbon.mod-left:hover:not(.is-collapsed) .side-dock-ribbon-action,
.side-dock-ribbon.mod-left:hover:not(.is-collapsed) .workspace-ribbon-collapse-btn svg {
    opacity: 1;
}
.side-dock-ribbon.mod-left:not(.is-collapsed) {
    flex: 0 0 5px;
    transition: flex .2s;
}
.side-dock-ribbon.mod-left:hover:not(.is-collapsed) {
    flex: 0 0 40px;
}

only one problem "Files icon" is behind fullscreen button:

@mawnir aaah I haven’t updated this snippet in a long time. I also never tested it on Mac. Just Windows 10

Just an FIY on version 1.6.7 on Windows :
The "Files" icon is hides behind the "Collapse" icon when the mouse hovers over it. The ribbon appears as intended but cannot access files anymore.