feat: implement dark mode

src/components/ThemeToggler/index.tsx

@@ -0,0 +1,13 @@
+import React from "react"
+import useTheme from "../../hooks/useTheme"
+import * as SC from "./styles"
+
+export function ThemeToggler() {
+  const { theme, toggleTheme } = useTheme()
+
+  return (
+    <SC.ThemeTogglerWrapper onClick={toggleTheme}>
+      <SC.Link>Switch to {theme === "dark" ? "light" : "dark"} mode</SC.Link>
+    </SC.ThemeTogglerWrapper>
+  )
+}

src/components/ThemeToggler/styles.tsx

@@ -0,0 +1,15 @@
+import { transparentize } from "polished"
+import styled from "styled-components"
+
+export const ThemeTogglerWrapper = styled.div``
+
+export const Link = styled.span`
+  display: inline-block;
+  cursor: pointer;
+  border-bottom: 2px solid transparent;
+
+  &:hover {
+    border-bottom: 2px solid
+      ${props => transparentize(0.6, props.theme.sidebar.foreground)};
+  }
+`