media breakpoints

                                    The Bootstrap grid system has four classes:
xs (for phones - screens less than 768px wide)
sm (for tablets - screens equal to or greater than 768px wide)
md (for small laptops - screens equal to or greater than 992px wide)
lg (for laptops and desktops - screens equal to or greater than 1200px wide)

                                    /* Answer to: "bootstrap media queries" */

/*
  Since Bootstrap is developed to be mobile first, the use a handful
  of media queries to create sensible breakpoints for their layouts
  and interfaces. These breakpoints are mostly based on minimum
  viewport widths and allow scaling up elements as the viewport
  changes.

  Bootstrap primarily uses the following media query ranges—or
  breakpoints—in their source Sass files for their layout, grid system,
  and components.
*/

/* Extra small devices (portrait phones, less than 576px) */
/* No media query for `xs` since this is the default in Bootstrap */`32`

/* Small devices (landscape phones, 576px and up) */
@media (min-width: 576px) { ... }

/* Medium devices (tablets, 768px and up) */
@media (min-width: 768px) { ... }

/* Large devices (desktops, 992px and up) */
@media (min-width: 992px) { ... }

/* Extra large devices (large desktops, 1200px and up) */
@media (min-width: 1200px) { ... }

                                    // Extra small devices (portrait phones, less than 576px)
// No media query for `xs` since this is the default in Bootstrap

// Small devices (landscape phones, 576px and up)
@media (min-width: 576px) { ... }

// Medium devices (tablets, 768px and up)
@media (min-width: 768px) { ... }

// Large devices (desktops, 992px and up)
@media (min-width: 992px) { ... }

// Extra large devices (large desktops, 1200px and up)
@media (min-width: 1200px) { ... }

                                     /* Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) {...}

/* Small devices (portrait tablets and large phones, 600px and up) */
@media only screen and (min-width: 600px) {...}

/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {...}

/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {...}

/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {...} 

                                    320px
480px
600px
768px
900px
1024px
1200px