Layer opacity controls how transparent or opaque a layer is. A layer with 0% opacity is completely transparent —and invisible— while a layer with 100% opacity is completely opaque. Lower it to reveal and blend with content behind it.
You can change the opacity of any layer: shapes, text, frames, groups or symbol instances. Select one or more layers, then drag the opacity 
slider in the Style section of the Inspector — or enter a value from 1 to 100 in the input field.
You can also separately adjust the opacity of Fills, Borders, Shadows, Inner Shadows, Tints and Text colors.
To change opacity, click and drag the slider or enter a value from 1 to 100 in the input field.
To apply a gradient-style fade to a layer, use the Fade effect 
instead. You can find it under Effects in the Inspector, or via Layer > Style > Add Fade.
