incorrect icon: Improve close / checkmark icon.

### Describe the Issue

Just a minor but somewhat annoying issue from a meticulous UI dev. Especially when using `close` and `checkmark` icon together. It seems that either the `close` is not correct or `checkmark`. You can decide.

### Comparison

| Type | Close | Checkmark | Compare | Comment |
| --- | :-: | :-: | :-: | --- |
| outline ||||Seems ok.|
| filled ||||The `close` appears too thick or the `checkmark` too thin.|
| sharp ||||Seems ok.|


We see that the `checkmark` outline and filled appear the same. The filled checkmark should be thicker or the cross thinner.