feat(ui): Implement Custom CSS configuration (#943)

* feat(ui): Implement Custom CSS configuration

* Update web/app/public/index.html

api/api.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/TwiN/gatus/v5/config"
+	"github.com/TwiN/gatus/v5/config/ui"
 	"github.com/TwiN/gatus/v5/config/web"
 	static "github.com/TwiN/gatus/v5/web"
 	"github.com/TwiN/health"
@@ -31,6 +32,10 @@ func New(cfg *config.Config) *API {
 		logr.Warnf("[api.New] nil web config passed as parameter. This should only happen in tests. Using default web configuration")
 		cfg.Web = web.GetDefaultConfig()
 	}
+	if cfg.UI == nil {
+		logr.Warnf("[api.New] nil ui config passed as parameter. This should only happen in tests. Using default ui configuration")
+		cfg.UI = ui.GetDefaultConfig()
+	}
 	api.router = api.createRouter(cfg)
 	return api
 }
@@ -87,6 +92,8 @@ func (a *API) createRouter(cfg *config.Config) *fiber.App {
 		statusCode, body := healthHandler.GetResponseStatusCodeAndBody()
 		return c.Status(statusCode).Send(body)
 	})
+	// Custom CSS
+	app.Get("/css/custom.css", CustomCSSHandler{customCSS: cfg.UI.CustomCSS}.GetCustomCSS)
 	// Everything else falls back on static content
 	app.Use(redirect.New(redirect.Config{
 		Rules: map[string]string{

api/api_test.go

@@ -25,6 +25,17 @@ func TestNew(t *testing.T) {
 			Path:         "/health",
 			ExpectedCode: fiber.StatusOK,
 		},
+		{
+			Name:         "custom.css",
+			Path:         "/css/custom.css",
+			ExpectedCode: fiber.StatusOK,
+		},
+		{
+			Name:         "custom.css-gzipped",
+			Path:         "/css/custom.css",
+			ExpectedCode: fiber.StatusOK,
+			Gzip:         true,
+		},
 		{
 			Name:         "metrics",
 			Path:         "/metrics",

api/custom_css.go

@@ -0,0 +1,14 @@
+package api
+
+import (
+	"github.com/gofiber/fiber/v2"
+)
+
+type CustomCSSHandler struct {
+	customCSS string
+}
+
+func (handler CustomCSSHandler) GetCustomCSS(c *fiber.Ctx) error {
+	c.Set("Content-Type", "text/css")
+	return c.Status(200).SendString(handler.customCSS)
+}