Vivaldi Browser Stylesheet

custom.css

/* vertical tabs use full height */

:root {
    --tab-width: 200px;
    --statusbar-height: 0px; 
    --toolbar-height: 30px;
    --neg-toolbar-height: -30px;
}

.native.tabs-left#browser :-webkit-any(.topmenu, .toolbar.toolbar-addressbar) {
    left: var(--tab-width);
    padding-right: calc(var(--tab-width) + 30px);
    padding-left: 0;
}

.native.tabs-right#browser :-webkit-any(.topmenu, .toolbar.toolbar-addressbar) {
    padding-right: var(--tab-width);
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser #tabs-container {
    height: calc(100vh - var(--statusbar-height)) !important;
    z-index: 1 !important;
    border-top: 1px #2F343F solid;
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .inner {
    top: var(--neg-toolbar-height) !important;
    overflow: visible !important;
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser #webview-container {
    top: var(--toolbar-height) !important;
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .toolbar.toolbar-addressbar {
    z-index: 1 !important;
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .toolbar,
:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .button-toolbar {
    height: 30px !important;
}

:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .toolbar .addressfield,
:-webkit-any(.native.tabs-left, .native.tabs-right)#browser .toolbar .searchfield {
    margin-top:   1px !important;
    margin-left:  3px !important;
    margin-right: 0   !important;
}

/* Remove header */
:-webkit-any(.native, .maximized)#browser #header {
    min-height: 0 !important;
}

/* Keep Vivaldi button */
:-webkit-any(.native, .maximized)#browser .vivaldi  {
    z-index: 2;
    top: 0 !important;
    left: auto !important;
    right: 0;
    width: 34px;
}

/* Keep horizontal menu */
:-webkit-any(.native, .maximized)#browser .topmenu {
    position: absolute;
}

/* grey Vivaldi button */
#browser #header .application-icon {
  filter: grayscale(100%);
}

/* hide unnecessary buttons */
.button-toolbar.back,
.button-toolbar.forward,
.button-toolbar.reload,
.button-toolbar.home {
  display: none !important;
}

#tabs-container.left  button.newtab,
#tabs-container.right button.newtab,
#tabs-container.left  .trash,
#tabs-container.right .trash,
#tabs-container.left  button.toggle-trash,
#tabs-container.right button.toggle-trash {
  left:    0  !important;
  width: 100% !important;
  padding: 0  !important;
}

#tabs-container.left  button.newtab svg,
#tabs-container.right button.newtab svg,
#tabs-container.left  button.toggle-trash svg,
#tabs-container.right button.toggle-trash svg {
  margin-left:  auto !important;
  margin-right: auto !important;
}

.tab-position .tab .tab-header {
  flex-basis:  29px !important;
  padding-top:    0 !important;
  padding-bottom: 0 !important;
  font-size:   12.5px !important;
}

.tab-position .tab.active {
  background-color: var(--colorHighlightBg) !important;
}

#browser.linux,
#browser.linux + div,
#browser.linux + div + div,
#browser.linux button,
#browser.linux input,
#browser.linux select,
#browser.linux textarea {
  font-family: "SF Compact Display", sans-serif !important;
}

Sorry to be thick, but please can you say what this does, and show a screenshot. Where should this be installed?