The max-width property sets the maximum width of an element. Note: The max-width property does not include padding, borders, or margins.
Value
Description
(numeric)
e.g. '400' would set the maximun width to 400 pixels (Microthemer automatically adds the 'px' unit if a unit isn't specified). Other commonly used units include 'em' and '%'. So you could enter '50%' in the Max Width field.
Max Width
The max-width property sets the maximum width of an element. Note: The max-width property does not include padding, borders, or margins.
Themeover CSS Reference
Online CSS References: Max Width
Online CSS Tutorials: Dimensions