By design Kendo UI widgets use primitives (i.e. different HTML elements in different widgets use the same CSS classes to provide a level of abstraction and allow common styling). Hence .k-edit-cell
classes will be applied to each cell / row in Kendo UI Grid when such is in edit mode.
Regarding your other question, to change the width of a texbox when editing a cell you can use the CSS snippet suggested by Dimiter. In order to change the DropDownList editor's width you should change the CSS selector (you can get the right selector as inspect the HTML output with any browser inspector). For example:
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