diff --git a/book.toml b/book.toml
index 93641a5..5ba9d37 100644
--- a/book.toml
+++ b/book.toml
@@ -5,4 +5,7 @@ multilingual = false
 src = "src"
 title = "Denops Documentation"
 
+[output.html]
+default-theme = "coal"
+
 [preprocessor.alerts]
diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 154fcdd..1fb53c8 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -17,4 +17,5 @@
   - [Properly create a virtual buffer](./tutorial/maze/properly-create-a-virtual-buffer.md)
   - [Properly configured the buffer](./tutorial/maze/properly-configured-the-buffer.md)
   - [Reduce the number of RPC calls](./tutorial/maze/reduce-the-number-of-rpc-calls.md)
+- [API Reference](./api-reference.md)
 - [FAQ](./faq.md)
diff --git a/src/api-reference.md b/src/api-reference.md
new file mode 100644
index 0000000..82f0904
--- /dev/null
+++ b/src/api-reference.md
@@ -0,0 +1,10 @@
+# API Reference
+
+There is a standard module [denops_std] to develop denops plugins. It provides
+various functions to interact with Vim and Neovim and some shorthands to make it
+easier to write plugins.
+
+You can find API references about the module by checking the Deno doc page:
+`https://deno.land/x/denops_std/mod.ts`.
+
+[denops_std]: https://deno.land/x/denops_std/mod.ts