I have a piece of code in my angular component:

```
    IncreaseFontSize()
    {
        let FontSize:any = document.body.style.fontSize;
        if(!FontSize)
        {
            FontSize = 1.4;
        }
        else
        {
            FontSize = parseFloat(FontSize);
        }
        document.body.style.fontSize = (FontSize+0.1) + 'rem';
    }

    DecreaseFontSize()
    {
        let FontSize:any = document.body.style.fontSize;
        if(!FontSize)
        {
            FontSize = 1.4;
        }
        else
        {
            FontSize = parseFloat(FontSize);
        }
        document.body.style.fontSize = (FontSize-0.1) + 'rem';
    }

```

These functions are called upon clicking two buttons, but it is not changing the font size of elements which have a font size already defined for them.

**I need to increase/decrease the font size of all elements**, i.e. if a label has font size 12px, a paragraph with font size of 11px, a div with font size 1.2rem the should increase their font size by 0.1 rem on click of the increase button.

How should I proceed with the approach?
Thanks in advance.