How to resize background images with css3

Transparency using RGBA

If you do not want to apply opacity to child elements, like in our example above, use RGBA color values.
The following example sets the opacity for the background color and not the text:

100% opacity

60% opacity

30% opacity

10% opacity

You learned from our CSS Colors Chapter, that you can use RGB as a color value. In addition to RGB,
you can use an RGB color value with an alpha channel (RGBA) — which specifies the opacity for a color.

An RGBA color value is specified with: rgba(red, green, blue, alpha). The
alpha parameter is a number between 0.0 (fully transparent) and 1.0 (fully opaque).

Tip: You will learn more about RGBA Colors in our CSS Colors Chapter.

Множественные фоны

Таблицы CSS позволяют сделать фон, состоящим из нескольких слоев изображений, количество которых определяется числом значений, вводимых последовательно через запятую после background-image. При этом картинки ложатся друг под друга сверху вниз, начиная с первого. Каждую из них можно определить с помощью указания значений других свойств, имеющих отношение к изображению. Присваивая слою состояние прозрачности, его можно скрывать.

Таким образом, установка значений свойств фона в CSS дает возможность окрасить его в любой цвет, приняв в учет различные элементы блока (свойства и ). Вместо этого или дополнительно внутри элемента можно поместить фоновое изображение, выбрав для него определенное место, увеличив или уменьшив при этом, а также при необходимости повторив его в горизонтальном или/и вертикальном направлении (свойства , , , , , ).

Следует иметь в виду, что рассмотренные свойства не наследуют своих родителей, но цвет фона наследника ввиду его значения по умолчанию, равного , будет таким же, как и родительский. Для наследования свойства необходимо устанавливать его в значение .

Notas

Se você estiver especificando um gradient como plano de fundo e tiver especificado um  junto, é melhor não especificar um tamanho que use um único componente setado como auto ou seja especificado usando apenas um valor de largura (por exemplo, ).  A renderização de gradients em tais casos mudou no Firefox 8 e, no momento, geralmente é inconsistente em todos os navegadores, pois nem todos implementam a renderização em total conformidade com a especificação do CSS3 e com a .

Observe que, em particular, não é recomendável usar uma dimensão de pixel e uma dimensões  com um gradient, porque é impossível replicar a renderização nas versões do Firefox antes de 8 e nos navegadores que não implementam a renderização do Firefox 8, sem saber o tamanho exato do elemento cujo plano de fundo está sendo especificado.

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quotes

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Possible Values

Here are the possible values:

Specifies that the background image should be scaled, while preserving its intrinsic aspect ratio (if any), to the largest size such that both its width and its height can fit inside the background positioning area.

Specifies that the background image should be scaled, while preserving its intrinsic aspect ratio (if any), to the smallest size such that both its width and its height can completely cover the background positioning area.

<length>

Specifies the size explicitly using a lenth value. For example, will result in a background image being scaled to 300 pixels wide and 100 pixels high.

The first value provided defines the width of the background image. The second value provides the height. If only one value is given, the second becomes .

For example, provides a width of 200 pixels and a height of 50 pixels. A value of will result in the width being 200 pixels and the height being automatically determined by using the image’s intrinsic ratio and the size of the other dimension, or failing that, using the image’s intrinsic size, or failing that, treating it as 100%. In other words, the image should keep its proportions as it scales (i.e. not get distorted).

<percentage>

Specifies the size explicitly using a percentage value. A percentage value is relative to the background positioning area — not to the original image size. For example, will result in a background image being scaled to 70 percent of the background positioning area.

As with the <length> values, the first value provides the width and the second provides the height. If the second value is missing, the height is automatically determined.

Specifies that the image size is automatically determined using the intrinsic width and/or height of the image.

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

Represents the value specified as the property’s initial value.

Represents the computed value of the property on the element’s parent.

This value acts as either or , depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

Property Values

Property Values

Примеры

Пример

Укажите размер фонового изображения в процентах:

#example1 {    background: url(mountain.jpg);   
background-repeat: no-repeat;    background-size: 100%
100%;}
#example2 {    background: url(mountain.jpg);   
background-repeat: no-repeat;    background-size: 75%
50%;}

Пример

Укажите размер фонового изображения с помощью «cover»:

#example1 {    background: url(mountain.jpg);   
background-repeat: no-repeat;    background-size: cover;
}

Пример

Укажите размер фонового изображения с помощью «contain»:

#example1 {    background: url(mountain.jpg);   
background-repeat: no-repeat;    background-size:
contain;}

Пример

Здесь у нас есть два фоновых изображения. Мы указываем размер первого фонового изображения с «contain», и второе фоновое изображение с& quot;cover»:

#example1 {    background: url(img_tree.gif), url(mountain.jpg);   
background-repeat: no-repeat;    background-size:
contain, cover;}

Property Values

Examples

The following are all valid syntaxes for the property.

/* keyword value syntax */
background-size: cover;
background-size: contain;

/* two-value syntax: first value specifies 
the width of the image and the second value 
specifies its height */
background-size: 50% auto;
background-size: 50px 30px;
background-size: 10em 12em;

/* one-value syntax: the second value is always 
assumed to be 'auto' */
background-size: 32em;
background-size: auto;
background-size: 100%;
                

The following are all examples of background image sizes specified with the property. The image in this example is assumed to be one with intrinsic dimensions and proportions (a JPEG image, for example);

/* stretch the image to fill the background 
area ignoring image ratio */
background-size: 100% 100%; 

/* the background image is shown at its intrinsic 
size */
background-size: auto; /* default */

/*  the background is shown with a width of 3em 
and its height is scaled proportionally to keep 
the original aspect ratio */
background-size: 3em; /* second value is assumed `auto` */

/* this one forces the background image to be 
15px by 15px */
background-size: 15px 15px;
                

The following example stretches the image so that exactly two copies fit horizontally (notice the values of the property and the property). The aspect ratio is preserved.

background-size: 50% auto;
background-repeat: repeat;
background-origin: border-box;
                

The following example specifies the background size of two background images. The first value specifies the size of the first image, and the second value specifies the size of the second image.

background-image: url(path/to/first/image.jpg), url(path/to/second/image.png);
background-size: 100% 100%, contain;
                

The following example will force the size of the gradient image to 100px by 100px.

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참고

If you use a as the background and specify a to go with it, it’s best not to specify a size that uses a single component, or is specified using only a width value (for example, ). Rendering of s in such cases changed in Firefox 8, and at present is generally inconsistent across browsers, which do not all implement rendering in full accordance with and with .

Note that it’s particularly not recommended to use a pixel dimension and an dimension with a , because it’s impossible to replicate rendering in versions of Firefox prior to 8, and in browsers not implementing Firefox 8’s rendering, without knowing the exact size of the element whose background is being specified.

CSS Properties

align-contentalign-itemsalign-selfallanimationanimation-delayanimation-directionanimation-durationanimation-fill-modeanimation-iteration-countanimation-nameanimation-play-stateanimation-timing-functionbackface-visibilitybackgroundbackground-attachmentbackground-blend-modebackground-clipbackground-colorbackground-imagebackground-originbackground-positionbackground-repeatbackground-sizeborderborder-bottomborder-bottom-colorborder-bottom-left-radiusborder-bottom-right-radiusborder-bottom-styleborder-bottom-widthborder-collapseborder-colorborder-imageborder-image-outsetborder-image-repeatborder-image-sliceborder-image-sourceborder-image-widthborder-leftborder-left-colorborder-left-styleborder-left-widthborder-radiusborder-rightborder-right-colorborder-right-styleborder-right-widthborder-spacingborder-styleborder-topborder-top-colorborder-top-left-radiusborder-top-right-radiusborder-top-styleborder-top-widthborder-widthbottombox-decoration-breakbox-shadowbox-sizingbreak-afterbreak-beforebreak-insidecaption-sidecaret-color@charsetclearclipclip-pathcolorcolumn-countcolumn-fillcolumn-gapcolumn-rulecolumn-rule-colorcolumn-rule-stylecolumn-rule-widthcolumn-spancolumn-widthcolumnscontentcounter-incrementcounter-resetcursordirectiondisplayempty-cellsfilterflexflex-basisflex-directionflex-flowflex-growflex-shrinkflex-wrapfloatfont@font-facefont-familyfont-feature-settingsfont-kerningfont-sizefont-size-adjustfont-stretchfont-stylefont-variantfont-variant-capsfont-weightgapgridgrid-areagrid-auto-columnsgrid-auto-flowgrid-auto-rowsgrid-columngrid-column-endgrid-column-gapgrid-column-startgrid-gapgrid-rowgrid-row-endgrid-row-gapgrid-row-startgrid-templategrid-template-areasgrid-template-columnsgrid-template-rowshanging-punctuationheighthyphensimage-rendering@importisolationjustify-content@keyframesleftletter-spacingline-heightlist-stylelist-style-imagelist-style-positionlist-style-typemarginmargin-bottommargin-leftmargin-rightmargin-topmask-imagemask-modemask-originmask-positionmask-repeatmask-sizemax-heightmax-width@mediamin-heightmin-widthmix-blend-modeobject-fitobject-positionopacityorderorphansoutlineoutline-coloroutline-offsetoutline-styleoutline-widthoverflowoverflow-wrapoverflow-xoverflow-ypaddingpadding-bottompadding-leftpadding-rightpadding-toppage-break-afterpage-break-beforepage-break-insideperspectiveperspective-originpointer-eventspositionquotesresizerightrow-gapscroll-behaviortab-sizetable-layouttext-aligntext-align-lasttext-decorationtext-decoration-colortext-decoration-linetext-decoration-styletext-indenttext-justifytext-overflowtext-shadowtext-transformtoptransformtransform-origintransform-styletransitiontransition-delaytransition-durationtransition-propertytransition-timing-functionunicode-bidiuser-selectvertical-alignvisibilitywhite-spacewidowswidthword-breakword-spacingword-wrapwriting-modez-index