src/vs/editor/contrib/peekView/browser/peekView.ts/PeekViewWidget/_applyStyles
class PeekViewWidget:	protected override _applyStyles(): void {
		super._applyStyles();
		const options = <IPeekViewOptions>this.options;
		if (this._headElement && options.headerBackgroundColor) {
			this._headElement.style.backgroundColor = options.headerBackgroundColor.toString();
		}
		if (this._primaryHeading && options.primaryHeadingColor) {
			this._primaryHeading.style.color = options.primaryHeadingColor.toString();
		}
		if (this._secondaryHeading && options.secondaryHeadingColor) {
			this._secondaryHeading.style.color = options.secondaryHeadingColor.toString();
		}
		if (this._bodyElement && options.frameColor) {
			this._bodyElement.style.borderColor = options.frameColor.toString();
		}
	}