2.2 How to limit the maximum width of the widget on desktop?

If the format "Classic look of comments" or "Comments inside frame" is chosen in the administration panel, the widget will have adaptive design and will always occupy 100% of the given width. You can specify the maximum width of the widget on desktop wrapping its code in <div> with certain sizes.
For example, <div class="tolstoycomments-feed" style="max-width:800px; margin: 0 auto;"></div>
If the format "Load widget in separate window" is chosen, you can specify certain sizes in the administration panel directly.

2.1 How to change the color theme of the widget and of its elements?

In the settings of the administration panel you can choose only general color theme. To specify certain colors you need to use theme parameter in the code. You can specify certain colors for the following elements:

/// javascript
function CreateTheme(color) { // color: 0-360 number
return {
colorBlack: "#000",
colorWrite: "#fff",
colorLink: `hsl(${color}, 44%, 52%)`,
colorLinkHover: `hsl(${color}, 44%, 40%)`,
colorLinkNoActive: `hsl(${color}, 26%, 36%)`,
colorLinkDark: `hsl(${color}, 44%, 76%)`,
colorCommentBgDefault: `hsl(${color}, 44%, 93%)`,
colorCommentSelect: `hsl(${color}, 43%, 85%)`,
colorCommentFocus: `hsl(${color}, 42%, 72%`,
colorBrend: `hsl(${color}, 45%, 71%)`,
colorRed: "#ef4c47"
};
}