Formatting Individuals headings

Im using the landscape gardening VW theme and I want to change the font size, colour and bold etc for the tagline on the homepage. How do I do this.

I tried typing the bleow code into Additional CSS howeve rit didn’t work
.tagline {
font-family: Arial;
font-size: 18px;
color: white!important;
font-weight: bold!important;
}

Also on the the slider main heading 1- I types in: Landscaping excellence, structural solutions, quality craftmanship (however nothing it appearing). Does anyone know how to fix this

Thank you