Make bottom panel tabs more visually distinct

[per1234]

When multiple panels are opened in the bottom panel, they are controlled by a tabs UI:

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🐛 There is very little visual contrast between the tabs:

🐛 The selected vs unselected tab color is almost the same.

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🐛 The tabs style is not consistent with the sketch tabs style:

🙂 Selected vs unselected sketch tabs have significantly different colors.

To Reproduce

1. Compile or upload a sketch to open the "Output" panel
2. Use Tools > Serial Monitor to open the "Serial Monitor panel
3. Use the downward pointing triangle menu > New Tab to create a second sketch tab

Expected behavior

• Bottom panel tabs are visually distinct from each other
• It is visually obvious which bottom panel tab is selected
• Consistent style of all tab UIs in the IDE

Desktop (please complete the following information):

• OS: Windows 10
• Version: 2.0.0-beta.12-nightly.20211115
  Date: 2021-11-15T03:03:14.165Z
  CLI Version: 0.19.1 alpha [718bbbf2]

[PerryBebbington]

@per1234
I agree with this but I do not agree that 'Selected vs unselected sketch tabs have significantly different colors'; they are just as bad (well, maybe not quite as bad but there is far too little contrast).