actually add custom scrollbar css

Author: rmorshea

docs/source/_static/css/better-scrollbar.css

@@ -0,0 +1,69 @@
+@media (prefers-color-scheme: dark) {
+  :root {
+    --scrollbar-thumb-color: #444;
+    --scrollbar-track-color: #223;
+  }
+}
+
+@media (prefers-color-scheme: light) {
+  :root {
+    --scrollbar-thumb-color: #ccc;
+    --scrollbar-track-color: #f8f8f8;
+  }
+}
+
+::-webkit-scrollbar {
+  width: 16px;
+  height: 16px;
+}
+
+::-webkit-scrollbar-corner,
+::-webkit-scrollbar-track {
+  background-color: var(--scrollbar-track-color);
+}
+
+::-webkit-scrollbar-thumb {
+  background-color: var(--scrollbar-thumb-color);
+  background-clip: padding-box;
+  border: 2px solid transparent;
+}
+
+/* Buttons */
+::-webkit-scrollbar-button:single-button {
+  background-color: var(--scrollbar-track-color);
+  display: block;
+  background-size: 10px;
+  background-repeat: no-repeat;
+}
+
+/* Up */
+::-webkit-scrollbar-button:single-button:vertical:decrement {
+  height: 12px;
+  width: 16px;
+  background-position: center 4px;
+  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='100' height='100' fill='var(--scrollbar-track-color)'><polygon points='50,00 0,50 100,50'/></svg>");
+}
+
+/* Down */
+::-webkit-scrollbar-button:single-button:vertical:increment {
+  height: 12px;
+  width: 16px;
+  background-position: center 2px;
+  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='100' height='100' fill='var(--scrollbar-track-color)'><polygon points='0,0 100,0 50,50'/></svg>");
+}
+
+/* Left */
+::-webkit-scrollbar-button:single-button:horizontal:decrement {
+  height: 12px;
+  width: 12px;
+  background-position: 3px 3px;
+  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='100' height='100' fill='var(--scrollbar-track-color)'><polygon points='0,50 50,100 50,0'/></svg>");
+}
+
+/* Right */
+::-webkit-scrollbar-button:single-button:horizontal:increment {
+  height: 12px;
+  width: 12px;
+  background-position: 3px 3px;
+  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='100' height='100' fill='var(--scrollbar-track-color)'><polygon points='0,0 0,100 50,50'/></svg>");
+}