Exercises — Stage 5: Experiment on the Branch

Exercise 1: Flip between themes

Goal: Feel that a branch checkout swaps your files.

Steps:

1. git checkout main. Reload the browser — light theme.
2. git checkout dark-theme. Reload — dark theme.
3. Repeat a few times.

What happened: Git rewrites style.css on disk each time you switch. The file literally has different content depending on which branch is checked out. This is safe because the commits on both branches preserve the version Git cares about.

Exercise 2: See both histories

Goal: Learn git log --all --graph.

Steps:

1. Run git log --all --oneline --graph.

What happened: You see every commit from every branch drawn as a small ASCII graph. The fork is visible: main and dark-theme share commits 1–3, then dark-theme has its own fourth commit.

Exercise 3: Tweak the accent color

Goal: Make one more change on the branch and verify main still does not care.

Steps:

1. On dark-theme, change #00ffcc to #ff0088 (hot pink) everywhere in style.css.
2. Save, reload — pink dark theme.
3. git checkout main — back to light theme, which never had any pink.
4. git checkout dark-theme — pink is still there because you never committed the change. Run git status to see it as uncommitted.
5. Run git restore style.css to undo the pink edit.

What happened: Uncommitted changes hang around between branch switches in some cases, but committed work is fully isolated. Experiment, and when you hate the result, throw it away with git restore.

Exercise 4: Compare the two branches

Goal: Learn git diff main..dark-theme.

Steps:

1. Run git diff main..dark-theme -- style.css.

What happened: Git prints a diff of style.css between main and dark-theme. Red lines are the light theme, green lines are the dark theme. This is how you ask "what does my experiment actually change?" without switching branches.