Walkthrough — Stage 6: Merge the Branch

This stage is about Git commands, not code.

Command: git checkout main

git checkout main

What's happening:

Switches your current branch to main. Git updates HEAD to point at main and rewrites any files on disk that differ between the two branches. In this case, style.css gets replaced with the light-theme version (because that is what the Stage 3 commit contains), and index.html stays the same (it never changed on dark-theme).

This is what lets you try something on a branch without risk — main is preserved, and you can return to it exactly as it was.

Command: git merge dark-theme

git merge dark-theme

What's happening:

git merge <branch> brings the commits from <branch> into your current branch. Because main had no new commits since dark-theme branched off, Git does the simplest possible merge: it moves the main label forward to the same commit dark-theme points at.

This is called a fast-forward merge. No merge commit is created — the history stays linear.

If main had gained its own commits in the meantime, Git would have created a merge commit with two parents. You do not hit that case here because nothing else touched main.

The result

After the merge:

• main points at the same commit as dark-theme.
• style.css on main is now the dark version.
• dark-theme still exists as a label. You could delete it with git branch -d dark-theme, but you do not have to.

Why this matters

Every real project uses branches for features and fixes, then merges them back to a main line. The mental picture you just built — "a branch is a safe place to try things, and merging brings it home" — is the entire mental model for team Git workflows.