It seems that the
height attributes determine the width or height of the canvas’s coordinate system, whereas the CSS properties just determine the size of the box in which it will be shown.
This is explained in the HTML specification:
canvaselement has two attributes to control the size of the element’s bitmap:
height. These attributes, when specified, must have values that are valid non-negative integers. The rules for parsing non-negative integers must be used to obtain their numeric values. If an attribute is missing, or if parsing its value returns an error, then the default value must be used instead. The
widthattribute defaults to 300, and the
heightattribute defaults to 150.