フロートする要素には幅を宣言しておく必要があります
In (x)HTML+CSS, floated elements need to have a width declared. Only elements with an intrinsic width (html, img, input, textarea, select, or object) are not affected
In (x)HTML+CSS, floated elements need to have a width declared. Only elements with an intrinsic width (html, img, input, textarea, select, or object) are not affected