I think Paypal moved/eliminated the "seller tools" when redesigning their site and user interface.
Now, on the top menu bar, if you sign into your business account, you will see your name in the upper left part of the menu bar. That has a dropdown menu to see your profile and account information, and to logout. To the LEFT of that is a "HELP" link. To the LEFT of "Help" is a "Dashboard" link that changes names depending on whether you are in the business area of your account or the DEVELOPER area.
When you sign into your business account, the page you are automatically taken to is the summary/activity/home page for your account that shows your Paypal balance, recent transactions, etc. The top menu navigation bar at the left will have your name/profile image with a dropdown menu to see your account and profile settings/info, and to logout. To the left of that is the "Help" link. To the left of that is a "Dashboard" link that will change depending on what section of your account you are signed into.
When you are in your regular "business" area where you can access your profile/emails/address, and Paypal transaction information, that "Dashboard" link in the menu bar will say "Developer." If you click on "Developer" you will be taken to the nitty-gritty underbelly of the back-end business side where you can customize invoices, get API credentials to link your account to an ecommerce website, etc. When you are in the "Developer" area, the "Dashboard" link in the menu bar will say "Business Dashboard" so that if you click on it, you will be taken back to the home/activity page where you can see your Paypal balance and transactions.
It appears Paypal has removed access to the PAYPAL CHECKOUT PAGE that you formerly could customize with a background color, logo, etc. This may have been done because the checkout process has been completely redesigned for better security and to streamline the process. There may be some place for you to upload your logo with a URL pointing to the checkout page, but for the life of me I cannot find it.
Hope this is of some help to whoever might be looking for this information like I was, two years after this question was originally asked and never answered.
