Reference: http://www.w3school.com.cn/cssref/pr_class_float.asp
Definition and usage
The Float property defines the direction in which the element floats. Historically, this property has always been applied to images, so that text surrounds the image, but in CSS, any element can float. A floating element generates a block-level box, regardless of its own element.
If floating non-replacement elements, specify a definite width; otherwise, they will be as narrow as possible.
Note: If there is only a small amount of space above a row for floating elements, then this element jumps to the next line, which continues until a row has enough space.
The value describes the left element floating to the left. The right element floats to starboard. None default value. The element does not float and appears in its position in the text. Inherit The value of thefloat property.
Default value: None.
(11) Learn the float property of CSS