diff --git a/README.md b/README.md
index 874ac56..33288c8 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,16 @@
 
     go run ./cmd/koushin imaps://mail.example.org:993 smtps://mail.example.org:465
 
+See `-h` for more information.
+
+## Themes
+
+They should be put in `public/themes/<name>/`.
+
+Templates in `public/themes/<name>/*.html` override default templates in
+`public/*.html`. Assets in `public/themes/<name>/assets/*` are served by the
+HTTP server at `themes/<name>/assets/*`.
+
 ## License
 
 MIT
diff --git a/cmd/koushin/main.go b/cmd/koushin/main.go
index d30cb85..e644884 100644
--- a/cmd/koushin/main.go
+++ b/cmd/koushin/main.go
@@ -1,28 +1,41 @@
 package main
 
 import (
+	"flag"
 	"fmt"
-	"os"
 
 	"git.sr.ht/~emersion/koushin"
+	"github.com/labstack/echo/v4"
 	"github.com/labstack/echo/v4/middleware"
+	"github.com/labstack/gommon/log"
 )
 
 func main() {
-	if len(os.Args) != 2 && len(os.Args) != 3 {
-		fmt.Println("usage: koushin <IMAP URL> [SMTP URL]")
-		return
+	var options koushin.Options
+	flag.StringVar(&options.Theme, "theme", "", "default theme")
+
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "usage: koushin [options...] <IMAP URL> [SMTP URL]\n")
+		flag.PrintDefaults()
 	}
 
-	imapURL := os.Args[1]
+	flag.Parse()
 
-	var smtpURL string
-	if len(os.Args) == 3 {
-		smtpURL = os.Args[2]
+	if flag.NArg() < 1 || flag.NArg() > 2 {
+		flag.Usage()
+		return
 	}
 
-	e := koushin.New(imapURL, smtpURL)
-	e.Use(middleware.Logger())
+	options.IMAPURL = flag.Arg(0)
+	options.SMTPURL = flag.Arg(1)
+
+	e := echo.New()
+	if l, ok := e.Logger.(*log.Logger); ok {
+		l.SetHeader("${time_rfc3339} ${level}")
+	}
+	if err := koushin.New(e, &options); err != nil {
+		e.Logger.Fatal(err)
+	}
 	e.Use(middleware.Recover())
 	e.Logger.Fatal(e.Start(":1323"))
 }
diff --git a/go.mod b/go.mod
index be3095a..1301e14 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/emersion/go-sasl v0.0.0-20190817083125-240c8404624e
 	github.com/emersion/go-smtp v0.12.0
 	github.com/labstack/echo/v4 v4.1.11
+	github.com/labstack/gommon v0.3.0
 	github.com/mattn/go-colorable v0.1.4 // indirect
 	github.com/mattn/go-isatty v0.0.10 // indirect
 	github.com/valyala/fasttemplate v1.1.0 // indirect
diff --git a/server.go b/server.go
index 021ecff..d9542b5 100644
--- a/server.go
+++ b/server.go
@@ -79,7 +79,7 @@ func (s *Server) parseSMTPURL(smtpURL string) error {
 	return nil
 }
 
-func NewServer(imapURL, smtpURL string) (*Server, error) {
+func newServer(imapURL, smtpURL string) (*Server, error) {
 	s := &Server{}
 
 	if err := s.parseIMAPURL(imapURL); err != nil {
@@ -310,12 +310,25 @@ func handleCompose(ectx echo.Context) error {
 	})
 }
 
-func New(imapURL, smtpURL string) *echo.Echo {
-	e := echo.New()
+func isPublic(path string) bool {
+	return path == "/login" || strings.HasPrefix(path, "/assets/") ||
+		strings.HasPrefix(path, "/themes/")
+}
+
+type Options struct {
+	IMAPURL, SMTPURL string
+	Theme            string
+}
 
-	s, err := NewServer(imapURL, smtpURL)
+func New(e *echo.Echo, options *Options) error {
+	s, err := newServer(options.IMAPURL, options.SMTPURL)
 	if err != nil {
-		e.Logger.Fatal(err)
+		return err
+	}
+
+	e.Renderer, err = loadTemplates(e.Logger, options.Theme)
+	if err != nil {
+		return fmt.Errorf("failed to load templates: %v", err)
 	}
 
 	e.HTTPErrorHandler = func(err error, c echo.Context) {
@@ -336,7 +349,7 @@ func New(imapURL, smtpURL string) *echo.Echo {
 			cookie, err := ctx.Cookie(cookieName)
 			if err == http.ErrNoCookie {
 				// Require auth for all pages except /login
-				if ctx.Path() == "/login" || strings.HasPrefix(ctx.Path(), "/assets/") {
+				if isPublic(ctx.Path()) {
 					return next(ctx)
 				} else {
 					return ctx.Redirect(http.StatusFound, "/login")
@@ -357,11 +370,6 @@ func New(imapURL, smtpURL string) *echo.Echo {
 		}
 	})
 
-	e.Renderer, err = loadTemplates()
-	if err != nil {
-		e.Logger.Fatal("Failed to load templates:", err)
-	}
-
 	e.GET("/mailbox/:mbox", func(ectx echo.Context) error {
 		ctx := ectx.(*context)
 
@@ -446,6 +454,7 @@ func New(imapURL, smtpURL string) *echo.Echo {
 	e.POST("/message/:mbox/:uid/reply", handleCompose)
 
 	e.Static("/assets", "public/assets")
+	e.Static("/themes", "public/themes")
 
-	return e
+	return nil
 }
diff --git a/template.go b/template.go
index 2581da0..f12e2ec 100644
--- a/template.go
+++ b/template.go
@@ -9,6 +9,7 @@ import (
 )
 
 type tmpl struct {
+	// TODO: add support for multiple themes
 	t *template.Template
 }
 
@@ -16,8 +17,8 @@ func (t *tmpl) Render(w io.Writer, name string, data interface{}, c echo.Context
 	return t.t.ExecuteTemplate(w, name, data)
 }
 
-func loadTemplates() (*tmpl, error) {
-	t, err := template.New("drmdb").Funcs(template.FuncMap{
+func loadTemplates(logger echo.Logger, themeName string) (*tmpl, error) {
+	base, err := template.New("").Funcs(template.FuncMap{
 		"tuple": func(values ...interface{}) []interface{} {
 			return values
 		},
@@ -25,5 +26,21 @@ func loadTemplates() (*tmpl, error) {
 			return url.PathEscape(s)
 		},
 	}).ParseGlob("public/*.html")
-	return &tmpl{t}, err
+	if err != nil {
+		return nil, err
+	}
+
+	theme, err := base.Clone()
+	if err != nil {
+		return nil, err
+	}
+
+	if themeName != "" {
+		logger.Printf("Loading theme \"%s\"", themeName)
+		if _, err := theme.ParseGlob("public/themes/" + themeName + "/*.html"); err != nil {
+			return nil, err
+		}
+	}
+
+	return &tmpl{theme}, err
 }