Allow customization of ApexCharts theming

[joshuaboniface]

Currently, the ApexCharts service charts are fixed in a "light" theme mode. When using a dark CSS style, this makes chart elements inconsistent and difficult to read. For example:

Note the font colour of the axis labels, as well as the light background of the selected menu.

Being able to change these options via CSS would be excellent.

[joshuaboniface]

Managed to find these via some inspection and trial-and-error:

.apexcharts-text tspan {
  fill: #ffffff;
}
.apexcharts-menu-open {
  background-color: #101b35;
}

That sets, respectively, the X- and Y-axis label colours, and the menu background colour.

But, this also opens up a whole other can of worms regarding styling of the Service status pages, which completely ignore the current theming due to a number of explicit CSS classes like text-black-50 bg-white applied to elements.