Hi Sattu Lahari,
There are two ways you can achieve this.
1 (Simple way). Enable Anonymous user and create a custom login page and style your login page accordingly.
Follow the academy link to create your Custom login page : CustomLoginPage
2. You can directly Customize in yourlogin.html page.
You can customize this as you like. You will see the loginpage’s logo has class ‘loginpage-logo’ and there will be a path specified in it. You can go to theme->Web and paste you logo there. Now go to your Login.html page and change the url path under the div containing loginpage-logo class.
For your reference :
You can always right-click inspect and hover the logo, it will show the class.
Hope this helps!!
You can modify Navigation Menu and the icon app