Width is 100%, zoom out window, right side of the area background picture becomes blank

You say the site is because the class named "Mkcont" the div is set to 1400px, when the width of the smaller window is less than 1400px, the actual BODY element width is not open to "1400px", but by itself set to "Browser visual window width" and " The maximum value in the Min-width property to resolve.
So all elements under the body set to 100% are equal to the values parsed by the body according to the above rules.
As you say the site solution is: Body set min-width= "1400px", or set all child elements in the body CSS property "width" or "min-width" property value must be less than the BODY element min-width, when all set " Width "Set 100% will be displayed normally.

Width is 100%, zoom out window, right side of the area background picture becomes blank