[Feature] Update styles

[replete]

I've written a CSS snippet to hack the styles into something that works better for me.

I will update the plugin styles in accordance with the general style I went for above.

Design features:

• Hidden scrollbar
• Full width panel size
• Hovering 'Track time' button
• Use CSS blending mode to brighten colours on light themes (same colours, just more muted)

TODO:

• Write new styles/markup in accordance with CSS snippet hack
• Make floating 'Track time' button look better