feat: Collapsible sidebar (#1721)

* wip

* styling, add keyboard shortcut

* tweak styling

app/components/Sidebar/components/CollapseToggle.js

@@ -0,0 +1,59 @@
+// @flow
+import { NextIcon, BackIcon } from "outline-icons";
+import * as React from "react";
+import { useTranslation } from "react-i18next";
+import styled from "styled-components";
+import Tooltip from "components/Tooltip";
+import { meta } from "utils/keyboard";
+
+type Props = {|
+  collapsed: boolean,
+  onClick?: () => void,
+|};
+
+function CollapseToggle({ collapsed, ...rest }: Props) {
+  const { t } = useTranslation();
+
+  return (
+    <Tooltip
+      tooltip={collapsed ? t("Expand") : t("Collapse")}
+      shortcut={`${meta}+.`}
+      delay={500}
+      placement="bottom"
+    >
+      <Button {...rest} aria-hidden>
+        {collapsed ? (
+          <NextIcon color="currentColor" />
+        ) : (
+          <BackIcon color="currentColor" />
+        )}
+      </Button>
+    </Tooltip>
+  );
+}
+
+export const Button = styled.button`
+  display: block;
+  position: absolute;
+  top: 28px;
+  right: 8px;
+  border: 0;
+  width: 24px;
+  height: 24px;
+  z-index: 1;
+  font-weight: 600;
+  color: ${(props) => props.theme.sidebarText};
+  background: ${(props) => props.theme.sidebarItemBackground};
+  transition: opacity 100ms ease-in-out;
+  border-radius: 4px;
+  opacity: 0;
+  cursor: pointer;
+  padding: 0;
+
+  &:hover {
+    color: ${(props) => props.theme.white};
+    background: ${(props) => props.theme.primary};
+  }
+`;
+
+export default CollapseToggle;

app/components/Sidebar/components/HeaderBlock.js

@@ -61,7 +61,7 @@ const Header = styled.button`
   display: flex;
   align-items: center;
   flex-shrink: 0;
-  padding: 16px 24px;
+  padding: 20px 24px;
   position: relative;
   background: none;
   line-height: inherit;