To alter the area style, open the area details page, and click 'Area Style' under 'Settings'. To change area colour and border colour, simply click the colour swatch, and select the desired colour. Click the check mark to save your selection. To change the border weight and type, hover your cursor over the label until the 'edit' option appears. Click 'edit', and select the desired border weight and type. Click the check mark to save your selection.
In the area details page, you can also edit the area shape. To do this, click 'Edit Shape' at the bottom of the Area Style menu. This will add editable points at regular intervals around the shape. Click and drag each of the points to alter the area shape. To add more points to any given segment, click the bright white points; to remove points, click on light grey points.
To change the size of a circular area, click 'edit' next to 'radius' in the Area Style menu. Type in your desired radius, in metres, and click the check mark to save your selection.