Learn how to find your way around in Lightroom panels by Expanding and Collapsing its disclosure Triangles
Throughout Lightroom small disclosure triangles appear in various places – click on these to display or hide that feature.
In the image, you would open the Split Toning panel by clicking on the topmost disclosure triangle.
Click the second marked triangle in the Detail panel to display the Sharpening preview window.
Look out for these triangles as they are often difficult to see but they can be used to hide and reveal important panels and other program features.