viewport and media query

<meta name="viewport" content="width=device-width">

start this tag.

<meta name="viewport" content="width=device-width,initial-scale=1">

1vmin = 1vm or 1vh, whichever is smallest
1vmax = 1vm or 1vh, whichever is largest

available media query expressions
width, height, device-width, device-height, orientation, aspect-ratio,
device-aspect-ratio, grid, color, color-index, monochrome, resolution, scan

.menu-items-grid {
    display: flex;
    flex-wrap: wrap;
    flex-direction: row;
    justify-content: space-around;
    padding: 0 1%
}

@media (orientation:portrait){
  .menu-items-grid {
    flex-direction: column;
  }
}

window.devicePixelRatio

@media (min-pixel-ratio:2){
  .pretteybackground {
    background: url('images/hires_bkg.png');
  }
}

cellular radio lifecycle
Idle -> active -> short sleep -> long sleep

-lifecycle of an HTTP request
DNS lookup -> socket connect -> HTTP request -> Data download

avoid redirect
minimize or eliminate render-blocking resources (stylesheets, fonts, unknown-size, image)

animation framework
settimeout, setInterval -> requestAnimationFrame

touch UI
hover does not rely on
use large hit target
do not disable mouse support

touch events
->touchstart, touchmove, touchend, touch cancel

Input
html5 has tel input type.

<input type="tel">

<label>
  <input type="checkbox">
  "Do you love lemurs?"
</label>