Style
                Styling the app is important for every appication. In
                NativeScript there are two possible option to attached style in
                the project. The most common way to style elements in the app is
                to define the styles inside CSS file and to set
                class name or id name to the components in the
                HTML, which you want to style. Another way is to
                attached styles in the TypeScript code, while using
                css property of the Page component.
              

Apply Style Via Code
Dynamically added styles
this.page.css = "#labelStyle{ background-color: #564448; color: white} button {font-size: 36; color: blue;}" +
                " .message {font-size: 36; color: #284848; text-align: center; margin: 0 20;}";
              Style Css File
Add style using CSS file
button, label, stack-layout {
    horizontal-align: center;    
}
button {
    font-size: 30;
}
.title {
    font-size: 25;
    margin: 20;
}
.message {
    font-size: 20;
    color: #284848;
    text-align: center;
    margin: 0 20;
} 
#labelStyle{
    background-color: #FFFF66;
}