style.css

/* CUSTOM PROPERTIES */
/* ================= */

:host {
  --tabgroup-background: #E7EAED;
  --tab-font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  --tab-font-size: 13px;
  --tab-background: #E7EAED;
  --tab-color: #696A6C;
  --tab-border-color: #DADCE0;
  --tab-transition: background-color 200ms ease-out, color 200ms ease-out;
  --tab-cursor: pointer;
  --tab-active-color: currentcolor;
  --tab-active-background: #FFF;
  --tag-hover-color: currentcolor;
  --tag-hover-background: #F1F3F4;
  --button-font-size: 15px;
  --button-background: none;
  --button-color: #696A6C;
  --button-hover-background: #DADCE0;
  --button-hover-color: #383a3e;
  --button-border-radius: 50%;
  --button-cursor: pointer;
  --badge-background: #383a3e;
  --badge-color: #fff;
  --close-button-visibility: visible;
}

/* STYLES */
/* ====== */

webview {
  position: absolute;
  visibility: hidden;
  width: 100%;
  height: 100%;
}

webview.visible {
  visibility: visible;
}

.etabs {
  font-family: var(--tab-font-family);
  text-rendering: optimizeLegibility;
  font-feature-settings: 'liga', 'clig', 'kern';
}

.nav {
  background: var(--tabgroup-background);
  box-shadow: inset 0 -1px var(--tab-border-color);
  border-top: 1px solid var(--tab-border-color);
  font-size: var(--tab-font-size);
  display: none;
  width: 100%;
  height: 32px;
  cursor: default;
  -webkit-user-select: none;
  user-select: none;
}

.nav.visible {
  display: flex;
}

.tabs {
  height: 100%;
}

.tab {
  background: var(--tab-background);
  box-shadow: inset 0 -1px var(--tab-border-color);
  color: var(--tab-color);
  cursor: var(--tab-cursor);
  font-size: var(--tab-font-size);
  transition: var(--tab-transition);
  display: none;
  position: relative;
  box-sizing: border-box;
  height: 100%;
  padding: 5px 9px;
  align-items: center;
}

.tab:first-child {
  border-left: none;
}

.tab.visible {
  display: inline-flex;
}

.tab.active {
  color: var(--tab-active-color);
  background: var(--tab-active-background);
	border-left: 1px solid var(--tab-border-color);
	border-right: 1px solid var(--tab-border-color);
	padding-left: 8px;
	padding-right: 8px;
  box-shadow: none;
}

.tab.active:last-child {
  border-right: none;
}

.tab.visible:not(.active)+.tab.visible:not(.active) {
	border-left: 1px solid var(--tab-border-color);
	padding-left: 8px;
}

.tab:not(.active):hover {
	background: var(--tab-hover-background);
  color: var(--tab-hover-color);
}

.tab-badge {
  background: var(--badge-background);
  color: var(--badge-color);
  text-align: center;
  border-radius: 5px;
  margin-left: 5px;
  padding: 1px 4px;
  font-size: 8px;
  font-weight: bold;
  line-height: 1.2;
}

.tab-badge.hidden {
  display: none;
}

.tab-icon {
  display: inline-block;
  height: 16px;
}

.tab-icon img {
  max-width: 16px;
  max-height: 16px;
}

.tab-title {
  display: inline-block;
  margin-left: 10px;
}

.tab-close {
  display: inline-block;
  margin-left: 10px;
}

.tab-close button {
  background: var(--button-background);
  border-radius: var(--button-border-radius);
  color: var(--button-color);
  cursor: var(--button-cursor);
  font-size: var(--button-font-size);
  display: inline-block;
  border: none;
  width: 20px;
  height: 20px;
  text-align: center;
  padding: 1px 0 0 0;
  visibility: var(--close-button-visibility);
}

.tab.active .tab-close button {
  visibility: visible;
}

.tab-close button:hover {
  color: var(--button-hover-color);
  background: var(--button-hover-background);
}

.buttons {
  display: flex;
  padding: 5px;
  border-left: 1px solid var(--tab-border-color);
}

.buttons button {
  color: var(--button-color);
  background: var(--button-background);
  border-radius: var(--button-border-radius);
	cursor: var(--button-cursor);
  font-size: var(--button-font-size);
  display: block;
  font-family: inherit;
  border: none;
  margin: 0;
  width: 20px;
  height: 20px;
  text-align: center;
  line-height: 1;
  padding: 1px 0 0 0;
}

.buttons button:hover {
  color: var(--button-hover-color);
  background: var(--button-hover-background);
}

.views {
  position: relative;
  height: calc(100vh - 33px);
}