How to animate a Border with its content, plus ComboBox (including dropdown)?

[Zakarayaev]

So I found this button animation trick on StackOverflow:

<Button.Styles>
    <Style Selector="Button">
        <Setter Property="FontSize" Value="14" />
    </Style>
    <Style Selector="Button:pointerover">
        <Setter Property="FontSize" Value="18" />
    </Style>
</Button.Styles>
<Button.Transitions>
    <Transitions>
        <DoubleTransition Property="FontSize" Duration="0:0:0.2" />
    </Transitions>
</Button.Transitions>

This works perfectly inside a Border – the button scales smoothly and the Border expands with it. Neat!

But how do I:

Animate text to smoothly grow from 14px to 22px (not just snap) while making its parent Border resize fluidly?

Do the same for ComboBox – animate its:

Main control (when idle/hovered)

Text/content inside

Dropdown list items

Add button color transitions where the color slides left-to-right on hover?