Time for action – creating the CSS file

Next we'll create our base CSS file named app.css. This will have all of the basic styling that will be used by our applications, such as the default font and colors. The first part of the CSS file contains some document-wide element styles that set the basic look and feel.

body
{
    font: 1em Verdana, Geneva, sans-serif;
    padding: 0;
    margin: 5px;
    color: Black;
    background-color: WhiteSmoke;
}
div
{
    padding: 0;
    margin: 0;
}
button
{
    cursor: pointer;
}
.hidden
{
    display: none;
}

First we set the style to be applied to the body, which will trickle down to the other elements. I like to set the font size to 1em instead of a fixed pixel size so that it uses the browser's default font size. Then you can base other measurements off of that using ems or percent to give you a more reactive layout and make it easier to change the look of your application later on. Constant pixel sizes are good when you always need something to be the same size no matter what, or for small values for borders and margins, and so on.

Next we make sure all padding and margins are removed from all the div elements, so we zero them out. It's also nice to have the cursor change to a pointer when the user hovers over a button, so we'll set that here too. Finally, there is a .hidden class selector that can be added to any element to hide it from being displayed.

We'll finish the CSS off with some styles for the app and main elements. All we're setting at this point are margins, padding, and colors:

#app
{
    margin: 4px;
    background-color: #bbc;
}
#app>header
{
    padding: 0 0.5em;
    font-size: 1.5em;
    color: WhiteSmoke;
    background-color: #006;
}
#app>footer
{
    padding: 0.25em;
    color: WhiteSmoke;
    background-color: #006;
}
#main
{
    margin: 1em;
}