Install extension in dev container.

.devcontainer/devcontainer.json

@@ -2,40 +2,23 @@
 // README at: https://github.com/devcontainers/templates/tree/main/src/docker-existing-docker-compose
 {
 	"name": "Existing Docker Compose (Extend)",
-
-	// Update the 'dockerComposeFile' list if you have more compose files or use different names.
-	// The .devcontainer/docker-compose.yml file contains any overrides you need/want to make.
 	"dockerComposeFile": [
 		"../docker-compose.yml",
 		"docker-compose.yml"
 	],
-
-	// The 'service' property is the name of the service for the container that VS Code should
-	// use. Update this value and .devcontainer/docker-compose.yml to the real service name.
 	"service": "server",
-
-	// The optional 'workspaceFolder' property is the path VS Code should open by default when
-	// connected. This is typically a file mount in .devcontainer/docker-compose.yml
 	"workspaceFolder": "/project",
-
+	"customizations": {
-	// Features to add to the dev container. More info: https://containers.dev/features.
+		"vscode": {
-	// "features": {},
+			"extensions": [
-
+				"arr.marksman",
-	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+				"mjmlio.vscode-mjml",
-	// "forwardPorts": [],
+				"davidanson.vscode-markdownlint",
-
+				"ecmel.vscode-html-css",
-	// Uncomment the next line if you want start specific services in your Docker Compose config.
+				"redhat.vscode-yaml",
-	// "runServices": [],
+				"yzhang.markdown-all-in-one"
-
+			]
-	// Uncomment the next line if you want to keep your containers running after VS Code shuts down.
+		}	
-	// "shutdownAction": "none",
+	},
-
-	// Uncomment the next line to run commands after the container is created.
-	// "postCreateCommand": "cat /etc/os-release",
-
-	// Configure tool-specific properties.
-	// "customizations": {},
-
-	// Uncomment to connect as an existing user other than the container default. More info: https://aka.ms/dev-containers-non-root.
 	"remoteUser": "root"
 }