days = np.arange(1, 7)
control = np.array([2.1, 2.4, 2.8, 3.0, 3.4, 3.7])
treatment = np.array([2.0, 2.7, 3.4, 4.1, 4.6, 5.0])

fig, ax = plt.subplots(figsize=(width_in, height_in), layout="constrained")
ax.plot(days, control, marker="o", linewidth=1.4, label="Control")
ax.plot(days, treatment, marker="s", linewidth=1.4, label="Treatment")
ax.set_title("Response over time")
ax.set_xlabel("Day")
ax.set_ylabel("Mean response")
ax.grid(True, linewidth=0.4, alpha=0.35)
ax.legend(frameon=False)