How do I implement responsive typography with Bootstrap 4? - responsive-design

Question

I'm building a responsive web app with Bootstrap 4. I want the font size of all text to be reduced on mobile devices compared to desktop, so I added the following to my base css file as per the Bootstrap documentation (https://getbootstrap.com/docs/4.0/content/typography/):
html {
font-size: 1rem;
}
#include media-breakpoint-up(sm) {
html {
font-size: 1.2rem;
}
}
#include media-breakpoint-up(md) {
html {
font-size: 1.4rem;
}
}
#include media-breakpoint-up(lg) {
html {
font-size: 1.6rem;
}
}
However the font size remains fixed. What am I doing wrong?

Answer 1

As of Bootstrap 4.3.1, there is now RFS (Responsive Font Sizing)! However, as explained in the docs, you must enable it using the $enable-responsive-font-sizes SASS variable.
RFS Demo: https://www.codeply.com/go/jr8RbeNf2M
Before Bootstrap 4.3.1, you'd can implement responsive text using SASS. However you need to specify the desired appropriate selector(s) for text that you want to resize...
#import "bootstrap/functions";
#import "bootstrap/variables";
#import "bootstrap/mixins";
html {
font-size: 1rem;
}
#include media-breakpoint-up(sm) {
html {
font-size: 1.1rem;
}
}
#include media-breakpoint-up(md) {
html {
font-size: 1.2rem;
}
}
#include media-breakpoint-up(lg) {
html {
font-size: 1.3rem;
}
}
#import "bootstrap";
Demo: https://www.codeply.com/go/5pZDWAvenE
This could also be done using CSS only (no SASS):
Demo: https://www.codeply.com/go/E1MVXqp21D

Answer 2

I think the easiest way is to use #media Queries. Suppose you want to change the font size responsively for a content with class "class-name" or even for entire html tag, just add your media queries to end of your css file or any place inside it.
Sample code:
/*
####################################################
M E D I A Q U E R I E S
####################################################
*/
/*
::::::::::::::::::::::::::::::::::::::::::::::::::::
Bootstrap 4 breakpoints
*/
/* Small devices (landscape phones, 544px and up) */
#media (min-width: 544px) {
.class-name {font-size: 16px;}
}
/* Medium devices (tablets, 768px and up) */
#media (min-width: 768px) {
.class-name {font-size: 30px;}
}
/* Large devices (desktops, 992px and up) */
#media (min-width: 992px) {
.class-name {font-size: 40px;}
}
/* Extra large devices (large desktops, 1200px and up) */
#media (min-width: 1200px) {
.class-name {font-size: 48px;}
}
more information can be found here

Answer 3

This is a Sass feature.
To have access to the media-breakpoint mixins and the size variables, you need to:
add a custom.scss file
#import "node_modules/bootstrap/scss/bootstrap";
and setup a Sass compiler
https://getbootstrap.com/docs/4.0/getting-started/theming/

Answer 4

Not a complete answer, but a good starting point is to enable responsive font sizes in v.4.5
$enable-responsive-font-sizes: true;
#import "../../../node_modules/bootstrap/scss/bootstrap";

Answer 5

Here is an alternative approach with loop
#import "bootstrap/functions";
#import "bootstrap/variables";
#import "bootstrap/mixins";
$font-sizes: (
html: ( xs: 1rem, sm: 1.2rem, md: 1.3rem),
);
#each $breakpoint in map-keys($grid-breakpoints) {
#include media-breakpoint-up($breakpoint) {
$infix: breakpoint-infix($breakpoint, $grid-breakpoints);
#each $name, $values in $font-sizes {
#each $n, $value in $values {
#if($infix == "-#{$n}" or ($infix == "" and $n == 'xs')) {
#{$name} { font-size: $value; }
}
}
}
}
}