Bootstrap framework components container, break points , padding, margin and rem

'rem' stands for 'root-element' size

Bootstrap 4 uses a default font-size of 16px, and its line-height is 1.5.

The default font-family is "Helvetica Neue", Helvetica, Arial, sans-serif.

In addition, all <p> elements have margin-top: 0 and margin-bottom: 1rem (16px by default).

Containers

There are 2 types of Containers

1. container : class provides a responsive fixed width container
2. container-fluid : class provides a full width container, spanning the entire width of the view port

Shorthand Classes

Assign responsive-friendly margin or padding values to an element or a subset of its sides with shorthand classes. Includes support for individual properties, all properties, and vertical and horizontal properties. Classes are built from a default Sass map ranging from .25rem to 3rem.

property is one of:

• m - for classes that set margin
• p - for classes that set padding

sides is one of:

• t - for classes that set margin-top or padding-top
• b - for classes that set margin-bottom or padding-bottom
• l - for classes that set margin-left or padding-left
• r - for classes that set margin-right or padding-right
• x - for classes that set both *-left and *-right
• y - for classes that set both *-top and *-bottom
• blank - for classes that set a margin or padding on all 4 sides of the elemen

size is one of:

• 0 - for classes that eliminate the margin or padding by setting it to 0
• 1 - (by default) for classes that set the margin or padding to $spacer * .25
• 2 - (by default) for classes that set the margin or padding to $spacer * .5
• 3 - (by default) for classes that set the margin or padding to $spacer
• 4 - (by default) for classes that set the margin or padding to $spacer * 1.5
• 5 - (by default) for classes that set the margin or padding to $spacer * 3
• auto - for classes that set the margin to auto

Container Padding

By default, containers have 15px left and right padding, with no top or bottom padding. Therefore, we often use spacing utilities, such as extra padding and margins to make them look even better. For example, .pt-3 means "add a top padding of 16px": (note that .pt-3 is equivalent to $spacer and $spacer is equal to rem, ie 16px. see table above)