Theme file CSS should use Variables instead of coded colors.

[xlcheese]

Could we convert the Mint theme file to use variables? The variables defined at the top of the CSS file? This could potentially allow a small app to give the user a color wheel to choose a custom color for the theme. There are currently 12 Mint y themes that have to be maintained. We could convert that to a single theme with colors defined as variables.

:root {
/* Core Theme Colors (Method 2: Comma-Separated RGB Channels) /
--theme-black-raw: 0, 0, 0; / #000000 /
--theme-toolbar-raw: 245, 245, 245; / #f5f5f5 /
--theme-text-raw: 48, 48, 48; / #303030 /
--theme-base-raw: 255, 255, 255; / #ffffff /
--theme-terracotta-raw: 196, 139, 121; / #C58A7A /
--theme-secondary-bg-raw: 250, 250, 250; / #fafafa /
--theme-accent-brown-raw: 196, 139, 121; / #c48b79 /
--theme-rubberband-fill-raw: 143, 110, 82; / #8f6e52 /
--theme-error-raw: 252, 65, 56; / #FC4138 /
--theme-border-raw: 199, 199, 199; / #c7c7c7 /
--theme-osd-raw: 64, 64, 64; / #404040 /
--theme-headerbar-raw: 219, 219, 219; / #dbdbdb /
--theme-input-border-raw: 186, 186, 186; / #BABABA /
--theme-warning-raw: 242, 120, 53; / #f27835 */
}