Frolin, within your example you are creating a text block that contain both Normal text & Normal text+ (i.e. Normal text+ = Normal text but altered)

Avoid this. Instead make your text block containing a mixture of Normal Text then Heading3 for example.

So in the example below the red text is Normal text. The black text is Heading3 and is larger italicized text.

Welcome to the home page for Marek Mountain a collection of websites by Florin Marek


Welcome to the home page for
Marek Mountain
a collection of websites by Florin Marek

The having done this avoid selecting the whole text line (it will show Many Styles) as you do in your example but just select a portion of the Normal text only, adjust as required and then select 'update Normal text in this variant'. Do the same by selecting just the Heading3 text and adjust and then select 'update Heading3 text in this variant'

I'd also go along with Chris's method of creating a new text style. This way you're only changing the text style within this block of text not the Normal text throughout the document. It's even worth considering creating standalone web site for this regularly edited content and loading it into your main website via a placeholder.