--- language: css contributors: - ["Mohammad Valipour", "https://github.com/mvalipour"] - ["Marco Scannadinari", "https://github.com/marcoms"] - ["Geoffrey Liu", "https://github.com/g-liu"] - ["Connor Shea", "https://github.com/connorshea"] - ["Deepanshu Utkarsh", "https://github.com/duci9y"] - ["Brett Taylor", "https://github.com/glutnix"] - ["Tyler Mumford", "https://tylermumford.com"] translators: - ["miky ackerman", "https://github.com/mikyackerman"] lang: es-es filename: learncss-es.css --- Paginas web estan contruidas en HTML, lo cual especifica el contenido de una pagina CSS(Hoja de Estilos en Cascada) es un lenguaje separado el cual especifica la **apariencia** de una pagina. codigo CSS esta hecho de *reglas* estaticas. Cada regla toma uno o mas *selectores* y da *valores* especificos a un numero de *propiedades* visuales. Esas propiedades estan entonces aplicadas a los elementos indicados en una pagina por los selectores Esta guia ha sido escrita con CSS 2 en mente, la cual es extendida por una nueva caracterica de CSS 3. **NOTA:** Debido a que CSS produce resultados visuales, para aprenderlo, necesitas Probar todo en un patio de juegos CSS como [dabblet] (http://dabblet.com/). El objetivo principal de este artículo es la sintaxis y algunos consejos generales. ## Sintaxis ```css /* Los comentarios aparecen dentro de un diagonal-asterisco, justo como esta linea no hay "comentarios en una linea"; este es el unico estilo de comentario.*/ /* #################### ## SELECTORS #################### */ /* el selector es usado para apuntar a un elemento de la pagina. */ selector { property: value; /* more properties...*/ } /* Here is an example element:
*/ /* You can target it using one of its CSS classes */ .class1 { } /* or both classes! */ .class1.class2 { } /* or its name */ div { } /* or its id */ #anID { } /* or using the fact that it has an attribute! */ [attr] { font-size:smaller; } /* or that the attribute has a specific value */ [attr='value'] { font-size:smaller; } /* starts with a value (CSS 3) */ [attr^='val'] { font-size:smaller; } /* or ends with a value (CSS 3) */ [attr$='ue'] { font-size:smaller; } /* or contains a value in a space-separated list */ [otherAttr~='foo'] { } [otherAttr~='bar'] { } /* or contains a value in a dash-separated list, e.g., "-" (U+002D) */ [otherAttr|='en'] { font-size:smaller; } /* You can combine different selectors to create a more focused selector. Don't put spaces between them. */ div.some-class[attr$='ue'] { } /* You can select an element which is a child of another element */ div.some-parent > .class-name { } /* or a descendant of another element. Children are the direct descendants of their parent element, only one level down the tree. Descendants can be any level down the tree. */ div.some-parent .class-name { } /* Warning: the same selector without a space has another meaning. Can you guess what? */ div.some-parent.class-name { } /* You may also select an element based on its adjacent sibling */ .i-am-just-before + .this-element { } /* or any sibling preceding it */ .i-am-any-element-before ~ .this-element { } /* There are some selectors called pseudo classes that can be used to select an element only when it is in a particular state */ /* for example, when the cursor hovers over an element */ selector:hover { } /* or a link has been visited */ selector:visited { } /* or hasn't been visited */ selected:link { } /* or an element is in focus */ selected:focus { } /* any element that is the first child of its parent */ selector:first-child {} /* any element that is the last child of its parent */ selector:last-child {} /* Just like pseudo classes, pseudo elements allow you to style certain parts of a document */ /* matches a virtual first child of the selected element */ selector::before {} /* matches a virtual last child of the selected element */ selector::after {} /* At appropriate places, an asterisk may be used as a wildcard to select every element */ * { } /* all elements */ .parent * { } /* all descendants */ .parent > * { } /* all children */ /* #################### ## PROPERTIES #################### */ selector { /* Units of length can be absolute or relative. */ /* Relative units */ width: 50%; /* percentage of parent element width */ font-size: 2em; /* multiples of element's original font-size */ font-size: 2rem; /* or the root element's font-size */ font-size: 2vw; /* multiples of 1% of the viewport's width (CSS 3) */ font-size: 2vh; /* or its height */ font-size: 2vmin; /* whichever of a vh or a vw is smaller */ font-size: 2vmax; /* or greater */ /* Absolute units */ width: 200px; /* pixels */ font-size: 20pt; /* points */ width: 5cm; /* centimeters */ min-width: 50mm; /* millimeters */ max-width: 5in; /* inches */ /* Colors */ color: #F6E; /* short hex format */ color: #FF66EE; /* long hex format */ color: tomato; /* a named color */ color: rgb(255, 255, 255); /* as rgb values */ color: rgb(10%, 20%, 50%); /* as rgb percentages */ color: rgba(255, 0, 0, 0.3); /* as rgba values (CSS 3) Note: 0 <= a <= 1 */ color: transparent; /* equivalent to setting the alpha to 0 */ color: hsl(0, 100%, 50%); /* as hsl percentages (CSS 3) */ color: hsla(0, 100%, 50%, 0.3); /* as hsl percentages with alpha */ /* Borders */ border-width:5px; border-style:solid; border-color:red; /* similar to how background-color is set */ border: 5px solid red; /* this is a short hand approach for the same */ border-radius:20px; /* this is a CSS3 property */ /* Images as backgrounds of elements */ background-image: url(/img-path/img.jpg); /* quotes inside url() optional */ /* Fonts */ font-family: Arial; /* if the font family name has a space, it must be quoted */ font-family: "Courier New"; /* if the first one is not found, the browser uses the next, and so on */ font-family: "Courier New", Trebuchet, Arial, sans-serif; } ``` ## Usage Save a CSS stylesheet with the extension `.css`. ```html
``` ## Precedence or Cascade An element may be targeted by multiple selectors and may have a property set on it in more than once. In these cases, one of the rules takes precedence over others. Rules with a more specific selector take precedence over a less specific one, and a rule occurring later in the stylesheet overwrites a previous one (which also means that if two different linked stylesheets contain rules for an element and if the rules are of the same specificity, then order of linking would take precedence and the sheet linked latest would govern styling) . This process is called cascading, hence the name Cascading Style Sheets. Given the following CSS: ```css /* A */ p.class1[attr='value'] /* B */ p.class1 { } /* C */ p.class2 { } /* D */ p { } /* E */ p { property: value !important; } ``` and the following markup: ```html

``` The precedence of style is as follows. Remember, the precedence is for each **property**, not for the entire block. * `E` has the highest precedence because of the keyword `!important`. It is recommended that you avoid its usage. * `F` is next, because it is an inline style. * `A` is next, because it is more "specific" than anything else. It has 3 specifiers: The name of the element `p`, its class `class1`, an attribute `attr='value'`. * `C` is next, even though it has the same specificity as `B`. This is because it appears after `B`. * `B` is next. * `D` is the last one. ## Media Queries CSS Media Queries are a feature in CSS 3 which allows you to specify when certain CSS rules should be applied, such as when printed, or when on a screen with certain dimensions or pixel density. They do not add to the selector's specificity. ```css /* A rule that will be used on all devices */ h1 { font-size: 2em; color: white; background-color: black; } /* change the h1 to use less ink on a printer */ @media print { h1 { color: black; background-color: white; } } /* make the font bigger when shown on a screen at least 480px wide */ @media screen and (min-width: 480px) { h1 { font-size: 3em; font-weight: normal; } } ``` Media queries can include these features: `width`, `height`, `device-width`, `device-height`, `orientation`, `aspect-ratio`, `device-aspect-ratio`, `color`, `color-index`, `monochrome`, `resolution`, `scan`, `grid`. Most of these features can be prefixed with `min-` or `max-`. The `resolution` feature is not supported by older devices, instead use `device-pixel-ratio`. Many smartphones and tablets will attempt to render the page as if it were on a desktop unless you provide a `viewport` meta-tag. ```html ``` ## Compatibility Most of the features in CSS 2 (and many in CSS 3) are available across all browsers and devices. But it's always good practice to check before using a new feature. ## Resources * [CanIUse](http://caniuse.com) (Detailed compatibility info) * [Dabblet](http://dabblet.com/) (CSS playground) * [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS) (Tutorials and reference) * [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/) (Reference) ## Further Reading * [Understanding Style Precedence in CSS: Specificity, Inheritance, and the Cascade](http://www.vanseodesign.com/css/css-specificity-inheritance-cascaade/) * [Selecting elements using attributes](https://css-tricks.com/almanac/selectors/a/attribute/) * [QuirksMode CSS](http://www.quirksmode.org/css/) * [Z-Index - The stacking context](https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context) * [SASS](http://sass-lang.com/) and [LESS](http://lesscss.org/) for CSS pre-processing * [CSS-Tricks](https://css-tricks.com)