* Make atom symbols black if atom is highlighted.
* Only do it for circle and continuous highlights.
* A lot of hash codes changed.
* Check hash code for new file.
* Change the highlighted atom to the same as carbon to accommodate dark mode, for example.
* Change the highlighted atom to the same as carbon to accommodate dark mode, for example. But get the logic right this time.
* Safer map lookup.
* Stackoverflow says this is better for >= C++17 as only one lookup.
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