At the moment critters doesn't correctly handle pseudo-class in the middle of the selector string and pseudo-class which take a value such as `:not`

Example
```
.mat-slider:hover .mat-slider-track-background
.mat-slider-min-value:not(.mat-slider-thumb-label-showing):hover.mat-slider-disabled .mat-slider-thumb
```

More context about CSS pseudo-classes can be found https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-classes

Closes GoogleChromeLabs#51

Class names can have `:` if they are escapped. Example: `.flex\:box`