Dynamic sidebar with userChrome.css

[sr-tream]

Basically this tweak from plugin TST, but with little mod, to use different width for tabs and other panels

/* Shrink sidebar until hovered, when using Tree Style Tab. */
:root {
    --thin-tab-width: 75px;
}
#sidebar-box:not() {
    min-width: var(--wide-tab-width) !important;
    max-width: none !important;
}
#sidebar-box {
    position: relative !important;
    transition: all 100ms !important;
    min-width: var(--thin-tab-width) !important;
    max-width: var(--thin-tab-width) !important;
}
#sidebar-box:hover {
    --wide-tab-width: 350px;
    transition: all 200ms !important;
    min-width: var(--wide-tab-width) !important;
    max-width: var(--wide-tab-width) !important;
    margin-right: calc((var(--wide-tab-width) - var(--thin-tab-width)) * -1) !important;
    z-index: 1;
}
#sidebar-box[sidebarcommand="_3c078156-979c-498b-8990-85f7987dd929_-sidebar-action"]:hover {
    --wide-tab-width: 200px;
    transition: all 200ms !important;
    min-width: var(--wide-tab-width) !important;
    max-width: var(--wide-tab-width) !important;
    margin-right: calc((var(--wide-tab-width) - var(--thin-tab-width)) * -1) !important;
    z-index: 1;
}
#main-window[inFullscreen] #sidebar-box,
#main-window[inFullscreen] #sidebar-splitter {
  display: none !important;
  width: 0px !important;
}
#main-window[titlepreface^="[1] "] #sidebar-box {
  visibility: collapse !important;
}