Checkbox label inside the checkbox or which button is activated?

I am searching for a solution to display something like this:

I want to create a HTML form where you can select multiple days per week. Like Monday, Tuesday and so on. On the image you can see the german shortcuts for the days.

I could realize that with checkboxes but here I would face the problem that it wouldn't look like the picture.. I want to have the labels inside the checkboxes. It should exactly like on the picture... Do you have any ideas, how I could do that?

My other idea was to create buttons and simply change the color if they got clicked... But how would I know which button got clicked/is selected?

I would appreciate any kind of help!

Kind regards