Defining base rules

Firstly, we will create a Base directory and place the reset styles in there:

./assets/css/Base/base.css

html { 
  -webkit-font-smoothing: antialiased; 
} 
 
* { 
  box-sizing: border-box; 
} 
 
nav > ul { 
  list-style: none; 
  padding: 0; 
  margin: 0; 
} 
 
body { 
  min-height: 100vh; 
  margin: 0; 
  font-family: Arial; 
} 
 
.is-hidden { 
  display: none !important; 
} 

For HTML scope, we will enable font smoothing for better font rendering.

Then, we will set box sizing of every element (*) in border-box. The default CSS box model is content-box, where width and height set to an element do not include padding and border. However, if we are setting, let's say, a sidebar width 250px, I would expect it to cover this length. With border-box, the box's size is always exactly what we set it, regardless of padding or border, but if you ask me, the border-box mode feels more natural.

We will reset indents and markers--for an unordered list--that are used for navigation (nav > ul). We make body element span the height of the entire viewport (min-height: 100vh), remove the default margin, and define the font family.

We will also introduce a global state is-hidden that can be applied on any element to remove it from the page flow. By the way, that is a good example of proactive and, therefore, permissible use of !important. By adding an is-hidden class (with JavaScript), we state that we want the element to hide, with no exceptions. Thus, we will never run into a specificity problem.