Chart headers allow viewers to perform several actions on charts, such as data export, drilling up or down, and view charts in explorer tools. Available across charts in Looker Studio (Formerly known as Data Studio) and the color is also customizable.
Always show: Header options are always visible. Table 1 in the above picture.
Show on hover (default): Hovering over the chart header shows three vertical dots. Click to access the header options. Table 2 in the above picture.
Don't show: Header options do not appear. However, report viewers can always access the options by right-clicking the chart. Table 3 in the above picture.