(1) Hide an element, and keep its :after or :before element

   #myspan {  
 #myspan:after {  

(2). CSS multiple background:

  html, body {
    background-image: url(01.png), url(z.jpg);
    background-repeat: repeat, no-repeat;
    background-position: 0 0;
    background-size: 3px 3px, cover;

(3) Bootstrap Navbar slide down not smooth

   <div class="navbar-collapse collapse in" id="navResponsive" aria-expanded="true" style="">
<ul class="nav navbar-nav">
<li class="dropdown">

After I added padding to #navResponsive, the slide down effect does not smooth. Maybe it affected the javascript or css.

(4) Change breakpoints to show collapsed navbar

//** Point at which the navbar becomes uncollapsed. $grid-float-breakpoint: $screen-md-min !default; //** Point at which the navbar begins collapsing. $grid-float-breakpoint-max: ($grid-float-breakpoint - 1) !default;

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