n-top
	+
		0 : border-top-width
	+
		0 : padding-top
	+
		150px : height
	+
		0 : padding-bottom
	+
		0 : border-bottom-width
	+
		50px : margin-bottom
	+
		50px : bottom
	=============
		350px  while the height of containing block is only 300px.

		So, here we definitely have an overconstrained situation. In which
		case the spec clearly states
		"If the values are over-constrained, ignore the value for 'bottom'
		and solve for that value."
		http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-height
