Lesson 7-2 covered the name for code that runs in the user's browser and makes the page interactive.
Frontend. Frontend code, meaning HTML, CSS, and JavaScript, runs on the user's device, and backend code runs on servers.
Those two words are about to become job titles.
The roles, in plain terms
Software engineering jobs mostly map onto the picture you built in unit 7:
| Role | Builds | Typical tools |
|---|---|---|
| Frontend engineer | What users see and click | HTML, CSS, JavaScript, TypeScript, React |
| Backend engineer | Servers, data, business logic | Python, Java, Go, SQL databases |
| Full-stack engineer | Both sides of one product | A mix of the two rows above |
| DevOps engineer | The machinery that builds, ships, and monitors everyone's code | Cloud platforms, Linux, automation scripts |
A typical day is not eight hours of typing code. Engineers read existing code, debug (lesson 1-1's word), review teammates' changes, write small tests, and spend a lot of time in discussions deciding what to build. The core skill under all of it is the one this course has been training: take a fuzzy goal, turn it into exact steps, and verify the result.
What is missing from a non-working login page
The missing work is backend work: a server must receive the login request and verify it against stored data.
Password checking has to happen on the backend, for two reasons. That is where the stored accounts live, and it is the only place users cannot tamper with the logic, since anything in the browser is running on the user's own device as lesson 7-2 noted.
The pretty page is frontend work, and it is already done here. The button exists, the layout is right, and nothing behind it is listening.
This split is worth recognizing because it describes a very common state of a half-built feature. A screen that looks finished can have no backend at all, and a working backend can have no screen, and neither half is a product on its own.
The engineer who works on both sides
That is a full-stack engineer.
The "stack" is the whole pile of technology a product sits on, from the browser code down to the database, and full-stack engineers move up and down it as needed.
In practice almost nobody is equally strong everywhere. Most full-stack engineers have a home side and enough range to finish a feature without waiting for someone else, which is the actual value of the title on a small team.
That range is also why this course covered both sides. Knowing that a request leaves a client, reaches a server, and comes back with data is what lets you reason about a whole feature instead of just your half of it.