Media query

body{
    background-image: url("img_tree.gif");
    background-repeat: no-repeat;
    background-attachment: fixed;
}

<style>

 .circle:before {
                    content: ' \25CF';
                    font-size: 50px;
                    color: black;
                }
</style>

<span class="circle"></span>

img {
  mask-image: url(‘mask.png’) linear-gradient(-45deg,
                        rgba(0,0,0,1) 20%, rgba(0,0,0,0) 50%);
  mask-image: url(#masking); /*referencing to the element generated and defined in SVG code*/
} 

/*EX:.container {
    padding: 0 15px;
// 576px window width and more
    @include sm {
        padding: 0 20px;
    }
// 992px window width and more
    @include lg {
        margin-left: auto;
        margin-right: auto;
        max-width: 1100px;
    } */

// Small tablets and large smartphones (landscape view)
$screen-sm-min: 576px;

// Small tablets (portrait view)
$screen-md-min: 768px;

// Tablets and small desktops
$screen-lg-min: 992px;

// Large tablets and desktops
$screen-xl-min: 1200px;


// Small devices
@mixin sm {
   @media (min-width: #{$screen-sm-min}) {
       @content;
   }
}

// Medium devices
@mixin md {
   @media (min-width: #{$screen-md-min}) {
       @content;
   }
}

// Large devices
@mixin lg {
   @media (min-width: #{$screen-lg-min}) {
       @content;
   }
}

// Extra large devices
@mixin xl {
   @media (min-width: #{$screen-xl-min}) {
       @content;
   }
}

 .rotate {

  transform: rotate(-90deg);


  /* Legacy vendor prefixes that you probably don
                                

.box-one {
	width: 100px;
	margin: 0 auto;
}

.box-two {
	width: 100px;
	margin-left: auto;
    margin-right: auto;
}

.truncate {
  width: 250px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

<div class="skt-hero"> <!--Inicia contenedor -->
<div class="columnas z1" style="--backgroundImg: url(https://cdn.thecoolist.com/wp-content/uploads/2016/05/Japanese-Cherry-beautiful-tree.jpg)">1ahola</div>
<div class="columnas z2" style="--backgroundImg: url(https://wallpaperstock.net/wonderful-trees-path-sun-light-wallpapers_47680_1920x1200.jpg)">2a</div>
<div class="columnas z3" style="--backgroundImg: url(https://img.culturacolectiva.com/featured_image/2018/10/04/1538678265674/deforestacion-del-bosque-amazonico-diecisiete-por-ciento.jpg)" >3a</div>
<div class="columnas z4" style="--backgroundImg: url(https://st.depositphotos.com/1012061/4434/i/600/depositphotos_44342021-stock-photo-sun-rays-inside-coconut-palms.jpg)">4a</div>
</div> <!-- Fin del contenedor -->

// css 

body{
z-index: -10:
} /* para asegurar que nadie este por debajo de body*/
.skt-hero {
    position: absolute;
    width: 100vw;
    height: 100vh;
    display: flex;
    background-image: url(https://haciendofotos.com/wp-content/uploads/las-mejores-fotos-de-paisajes-2020.jpg);
    background-size: cover;
}
.skt-hero:hover{
    z-index:-3;
}
.columnas {
    width: 25%;
    height: 100%;
    border: 1px solid gray;
    background-color: transparent;
    position:absolute;
    opacity: 0.05;
    transition: opacity 2s ease;
}
.columnas:hover {
    height: 100%;
    width:100vw;
    background-image: var(--backgroundImg);
    position: ;
    z-index: -1;
    background-size: cover;
    opacity: 1;
}
.z1{
left:0%;
}
.z1:hover{
left:0%;
}
.z2{
left:25%;
}
.z2:hover{
left:0%;
}
.z3{
left:50%;
}
.z3:hover{
left:0%;
}
.z4{
left:75%;
}
.z4:hover{
left:0%;
}

javascript:(d=>{var css=`:root{background-color:#f1f1f1;filter:invert(1) hue-rotate(180deg)}img:not([src*=".svg"]),picture,video{filter: invert(1) hue-rotate(180deg)}`,style,id="dark-mode",ee=d.getElementById(id);if(null!=ee)ee.parentNode.removeChild(ee);else {style = d.createElement('style');style.type="text/css";style.id=id;if(style.styleSheet)style.styleSheet.cssText=css;else style.appendChild(d.createTextNode(css));(d.head||d.querySelector('head')).appendChild(style)}})(document)

<h1 class="ribbon">
   <strong class="ribbon-content">Everybody loves ribbons</strong>
</h1>

.dynamic-shadow {

  position: relative;

  width: rem;

  height: 10rem;

  background: linear-gradient(5deg, #d7ff, #00ffb8);
6
  z-index: 1;
7
}
8
.dynamic-shadow::after {

  content: '';
10
  width: 100%;

  height: 100%;

  position: absolute;

  background: inherit;

  top: 0.5rem;

  filter: blur(0.4rem);

  opacity: 0.7;

  z-index: -1;

}

​

 add_filter( 'jetpack_sharing_counts', '__return_false', 99 );
add_filter( 'jetpack_implode_frontend_css', '__return_false', 99 );
                                

ol li {
	 list-style-type: none;
     }
     
// OR

li {
	list-style-type: none;
}

.gradient {
  background-image:
    linear-gradient(
      to right, 
      red, 
      blue,
      yellow, 
      green
    );
}

<!--ESTILOS:
- Toda la barra se llama: scrollbar(barra = en ingles "bar")
- thumb: se le llama al pulgar que esta dentro
- track: se le llama al camino, pista.
Entonces cuendo quieras editar solo tienes que combinar:
::-webkit-scrollbar{}
::-webkit-scrollbar-thumb{}
::-webkit-scrollbar-track{}
A todos puedes aplicarles: puedes aplicarle border-radious, background, etc..
EXEPTO: dimenciones como whidth(esto le corresponde a la barra (scrollbar)).
NOTA: primero se deve editar(aunque sea minimo) scrollbar sino no correra las ediciones de los 
      otros componentes     
-->

<!--TRANSICIÓN: Se le denomina Smooth Scroll al efecto de transición
-CSS: scroll-behavior: smooth; para transiciones suabes
  html {
  scroll-behavior: smooth; // se le aplica al elemento que genera el scroll, ejemp la pagina.
  }
-Javascript: 
  window.scroll({
    top: 2500, 
    left: 0, 
    behavior: 'smooth'
  }); // aplicado a la ventana principal. vea el link hay otro caso
-->