The menu bar contains four main groups of controls:
This can be clicked to temporarily toggle the visibility of all the open panels at once and expose the full preview area.
Alternatively pressing ESC on the keyboard will have the same effect.
The four buttons open and close the corresponding panel, highlighting which ones are open even when they are not visible. In devices with small screens these buttons will shrink showing only the icons.
The screen size selector is composed of a draggable slider which adjusts the width of the preview area to simulate smaller screen sizes. Next there are clickable icons, they are the presets for a standard mobile, tablet or desktop computer size.
The last control is a color picker that allows you to change the background color of the preview area.
This is useful in case the slider will be placed on a page, post or widget area with a particular background color.
In this way you can see if the slider color scheme will fit with it.