Bootstrap use css class at breakpoint (xs,md...)

Question

Is there a way to use the bootstrap breakpoints xs,md etc. as a condition for assigning classes?

Example:

<span class="text-large-md text-small-xs">My Text</span>

I just want to be flexible assigning classes, depending on which screensize (breakpoint) I am.

Update: Bootstrap has helper classes like hidden-xs. So if you want to hide a text on a button on small screens you can use this class. But if the button for instance uses a fix width (assigned by a class), the button size won't change. So my question is, how to change class styles depending on the screen size, via bootstrap.

Answer 1

You could write something like this with LESS (if you're compiling with Bootstrap's LESS):

// Responsive text
/**
  * Bootstrap's LESS variables:
      @screen-sm-min:   768px;
      @screen-md-min:   992px;
      @screen-lg-min:   1200px;
      @font-size-base:  14px;
      @font-size-small: ceil((@font-size-base * 0.85)); // ~12px
      @font-size-large: ceil((@font-size-base * 1.25)); // ~18px
  */

.text-xs-small    { font-size: @font-size-small; }
.text-xs-large    { font-size: @font-size-large; }

@media (min-width: @screen-sm-min) {
  .text-sm-small  { font-size: floor((@font-size-small * 1.1)); }
  .text-sm-large  { font-size: floor((@font-size-large * 1.1)); }
}

@media (min-width: @screen-md-min) {
  .text-md-small  { font-size: floor((@font-size-small * 1.3)); }
  .text-md-large  { font-size: floor((@font-size-large * 1.3)); }
}

@media (min-width: @screen-lg-min) {
  .text-lg-small  { font-size: floor((@font-size-small * 1.5)); }
  .text-lg-large  { font-size: floor((@font-size-large * 1.5)); }
}

Or just CSS:

.text-xs-small {
  font-size: 12px;
}
.text-xs-large {
  font-size: 18px;
}
@media (min-width: 768px) {
  .text-sm-small {
    font-size: 13px;
  }
  .text-sm-large {
    font-size: 19px;
  }
}
@media (min-width: 992px) {
  .text-md-small {
    font-size: 15px;
  }
  .text-md-large {
    font-size: 23px;
  }
}
@media (min-width: 1200px) {
  .text-lg-small {
    font-size: 18px;
  }
  .text-lg-large {
    font-size: 27px;
  }
}

Answer 2

Since Bootstrap writes their source CSS in Sass, all their media queries are available via Sass mixins.

To answer your question, Bootstrap suggests you do it this way:

html {
  font-size: 14px;
}

@include media-breakpoint-up(sm) {
  html {
    font-size: 16px;
  }
}

@include media-breakpoint-up(md) {
  html {
    font-size: 20px;
  }
}

@include media-breakpoint-up(lg) {
  html {
    font-size: 28px;
  }
}

Another example from Bootstrap's site:

@include media-breakpoint-up(xs) { ... }
@include media-breakpoint-up(sm) { ... }
@include media-breakpoint-up(md) { ... }
@include media-breakpoint-up(lg) { ... }
@include media-breakpoint-up(xl) { ... }

// Example usage:
@include media-breakpoint-up(sm) {
  .some-class {
    display: block;
  }
}

Answer 3

The recommended approach looks good from @livelytania - in the past for a pure HTML/bootstrap solution I've done

<div class="...">
    <div class="d-none d-xl-block css-class-for-xl">Display me when xl</div>
    <div class="d-block d-xl-none css-class-for-lt-xl">Display me when less than xl</div>
</div>