To understand how to style things, you have to understand how the DOM is set up. When we write an app simple form component, in the DOM you'll see app simple form and then nested inside of it you'll see a div and then inside of that div you'll see an input and a button.
Although you might be used to writing divs inside of frameworks when you build a component to represent the outer element of that component, you actually don't need to do that because this input and button will be wrapped inside of this app simple form. We can add styles here, so we'll say styles. This is an array of strings.
Then I can add a style to app simple form. I'll just add a style of margin bottom 10 pixels.
When I do this, you won't see anything change over here. There's no margin bottom applied to it. That's because our component doesn't have any display to find. Meaning that on our app simple form, which we can reference in here through host, we need to define a display such as block or I'm going to choose flex.
Once I choose a display for my component, the type of display I want it to have, now it can represent that margin bottom and it will know how to apply it based on this display. I also want this input and the button to be on top of each other, so I'm going to choose flex direction column. Hit save. Now these are on top of each other.
You can see that inside of our component a host will refer to our component, which in the DOM is represented by this app simple form. Outside of the component, app simple form can be selected by using the element selector of it or by giving it a class or any other traditional method of selecting it.
The other piece here I need to show is that if I want to select everything, every selector inside of my component and I wanted everything to have a font family of monospace and I hit save. In a traditional page this would select every element inside and outside of this component. It would select it across your entire app.
You can see it's isolating this and this font family to only the items, the input, and the button that are inside of my component. It's not affecting this stuff outside of my component.
The styles you define inside your component will be isolated to that component. If I wanted to say input, focus. When I focus, I want the font wait to be bold. I can know and trust that only in these components and these inputs will the font turn bold when I click on them.
Just a couple other things I want to clean up. I want the outline to be none and I want my button, border to be none just to make my components nice and clean.