Modal color update

[ykamendrovskiy]

All the floating items now have the same color --yc-color-base-float but in fact we have two classes of float items — modals and popups. Modals are the ones displayed on top of a veil thet mutes the page. And popups are the ones with a shadow like lists in selects, suggests etc.

In dark mode all the backgrounds are dark and in some modals we display popups and the shadow doesn't work well to separate these items.

So, let's have another semantic variable for the modals — all the floating components with a veil.

1. Let's create a new semantic variable --yc-color-base-modal

• light theme: --yc-color-private-white-1000
• dark theme: --yc-color-private-black-rock-850

2. Let's assign this variable as a background for the modal

3. Let's change the veil color --yc-color-sfx-veil in dark theme to optimize modal readability

• add new private variable --yc-color-private-black-600 with value rgba(0, 0, 0, .6)
• assign this variable as a value in dark theme