<thead> 标签HTML 的 <thead> 元素定义了一组定义表格的列头的行。
align（废弃）: This enumerated attribute specifies how horizontal alignment of each cell content will be handled. Possible values are:
left , aligning the content to the left of the cell
center , centering the content in the cell
right , aligning the content to the right of the cell
justify , inserting spaces into the textual content so that the content is justified in the cell
char , aligning the textual content on a special character with a minimal offset, defined by the char and charoff attributes. If this attribute is not set, the left value is assumed.
bgcolor: This attribute defines the background color of each cell of the column. It is one of the 6-digit hexadecimal code as defined in sRGB, prefixed by a '#'. One of the sixteen predefined color strings may be used.
char（废弃）: This attribute is used to set the character to align the cells in a column on. Typical values for this include a period (.) when attempting to align numbers or monetary values. If align is not set to char, this attribute is ignored.
charoff（废弃）: This attribute is used to indicate the number of characters to offset the column data from the alignment characters specified by the char attribute.
valign（废弃）: This attribute specifies the vertical alignment of the text within each row of cells of the table header. Possible values for this attribute are:
baseline , which will put the text as close to the bottom of the cell as it is possible, but align it on the baseline of the characters instead of the bottom of them. If characters are all of the size, this has the same effect as bottom.
bottom , which will put the text as close to the bottom of the cell as it is possible;
middle , which will center the text in the cell;
top , which will put the text as close to the top of the cell as it is possible.