Adding Extra custom Title styles

I added extra css for some Heading styles for optimal SEO reasons and not use the H1 to H4 tags multiple times. I added HeadingC1 to Heading C4 in this Plugin. The problem is that only the headingC1 works.

What am I doing wrong;

HeadingC1 – – span – headingcustom1 – I added css
HeadingC2 – – span – headingcustom2 – I added css
HeadingC3 – – span – headingcustom3 – I added css
HeadingC4 – – span – headingcustom4 – I added css

css – f.e.
span.headingcustom4 {
font-size: 21px;
line-height: 29px;
font-weight: 300;
margin-bottom: 18px;
}

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