Revert "doc/website: migrate to docusaurus v2 (#1382)" (#1383)

This reverts commit 21c3fa83fc.

doc/website/static/css/code-block-buttons.css

@@ -0,0 +1,39 @@
+/* "Copy" code block button */
+pre {
+    position: relative;
+}
+
+pre .btnIcon {
+    position: absolute;
+    top: 4px;
+    z-index: 2;
+    cursor: pointer;
+    border: 1px solid transparent;
+    padding: 0;
+    color: #fff;
+    background-color: transparent;
+    height: 30px;
+    transition: all .25s ease-out;
+}
+
+pre .btnIcon:hover {
+    text-decoration: none;
+}
+
+.btnIcon__body {
+    align-items: center;
+    display: flex;
+}
+
+.btnIcon svg {
+    fill: currentColor;
+    margin-right: .4em;
+}
+
+.btnIcon__label {
+    font-size: 11px;
+}
+
+.btnClipboard {
+    right: 10px;
+}