Best way to include CSS Why use import

Question

Basically I am wondering what is the advantage   purpose of using  import to import stylesheets into an existing stylesheet versus just adding another       lt link rel  stylesheet  type  text css  href      gt    to the head of the document

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There are many GOOD reasons to use  import   One powerful reason for using  import is to do cross-browser design  Imported sheets  in general  are hidden from many older browsers  which allows you to apply specific formatting for very old browsers like Netscape 4 or older series  Internet Explorer 5 2 for Mac  Opera 6 and older  and IE 3 and 4 for PC   To do this  in your base css file you could have the following    import  newerbrowsers css    body     font-size 13px      In your imported custom sheet  newerbrowsers css  simply apply the newer cascading style   html body     font-size 1em      Using  em  units is superior to  px  units as it allows both the fonts and design to stretch based on user settings  where as older browsers do better with pixel-based  which are rigid and cannot be changed in browser user settings   The imported sheet would not be seen by most older browsers   You may so  who cares  Try going to some larger antiquated government or corporate systems and you will still see those older browsers used  But its really just good design  because the browser you love today will also someday be antiquated and outdated as well  And using CSS in a limited way means you now have an even larger and growing group of user-agents that dont work well with you site   Using  import your cross-browser web site compatibility will now reach 99 9  saturation simply because so many older browser wont read the imported sheets  It guarantees you apply a basic simple font set for their html  but more advanced CSS is used by newer agents  This allows content to be accessible for older agents without compromising rich visual displays needed in newer desktop browsers   Remember  modern browsers cache HTML structures and CSS extremely well after the first call to a web site  Multiple calls to the server is not the bottleneck it once was   Megabytes and megabytes of Javascript API s and JSON uploaded to smart devices and poorly designed HTML markup that is not consistent between pages is the main driver of slow rendering today  Youre average Google news page is over 6 megabytes of ECMAScript just to render a tiny bit of text  LOL  A few kilobytes of cached CSS and consistent clean HTML with smaller javascript footprints will render in a user-agent in lightning speed simply because the browser caches both consistent DOM markup and CSS  unless you choose to manipulate and change that via javascript circus tricks

User · Answer

using the link method  the stylesheets are loaded parallel  faster and better   and nearly all browsers support link  import loads any extra css files one-by-one  slower   and could give you Flash Of Unstyled Content

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Quoted from http   webdesign about com od beginningcss f css import link htm     The main purpose of  import method is to use multiple style sheets on a page  but only one link in your  lt  head    For example  a corporation might have a global style sheet for every page on the site  with sub-sections having additional styles that only apply to that sub-section  By linking to the sub-section style sheet and importing the global styles at the top of that style sheet  you don t have to maintain a gigantic style sheet with all the styles for the site and every sub-section  The only requirement is that any  import rules need to come before the rest of your style rules  And remember that inheritance can still be a problem

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It is best to NOT use  import to include CSS in a page for speed reasons  See this excellent article to learn why not  http   www stevesouders com blog 2009 04 09 dont-use-import   Also it is often harder to minify and combine css files that are served via the  import tag  because minify scripts cannot  peel out  the  import lines from other css files  When you include them as  lt link tags you can use existing minify php dotnet java modules to do the minification   So  use  lt link   gt  instead of  import

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I think  import is most useful when writing code for multiple devices  Include a conditional statement to only include the style for the device in question  then only one sheet gets loaded  You can still use the link tag to add any common style elements

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Use  import in your CSS if you are using a CSS RESET  like Eric Meyer s Reset CSS v2 0  so it does it s job before applying your CSS  thus preventing conflicts

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I m going to play devil s advocate  because I hate it when people agree too much   1  If you need a stylesheet that depends on another one  use  import  Do the optimization in a separate step   There are two variables you re optimizing for at any given time - the performance of your code  and the performance of the developer  In many  if not a majority of cases  it s more important to make the developer more efficient  and only then make the code more performant   If you have one stylesheet that depends on another  the most logical thing to do is to put them in two separate files and use  import  That will make the most logical sense to the next person who looks at the code       When would such a dependency happen  It s pretty rare  in my opinion   - usually one stylesheet is enough  However  there are some logical places to put things in different CSS files           Theming  If you have different color schemes or themes for the same page  they may share some  but not all components    Subcomponents  A contrived example - say you have a restaurant page that includes a menu  If the menu is very different from the rest of   the page  it ll be easier to maintain if it s in its own file       Usually stylesheets are independent  so it s reasonable to include them all using  lt link href gt   However  if they are a dependent hierarchy  you should do the thing that makes the most logical sense to do   Python uses import  C uses include  JavaScript has require  CSS has import  when you need it  use it   2  Once you get to the point where the site needs to scale  concatenate all the CSS   Multiple CSS requests of any kind - whether through links or through  imports - are bad practice for high performance web sites  Once you re at the point where optimization matters  all your CSS should be flowing through a minifier  Cssmin combines import statements  as  Brandon points out  grunt has multiple options for doing so as well   See also this question    Once you re at the minified stage   lt link gt  is faster  as people have pointed out  so at most link to a few stylesheets and don t  import any if at all possible   Before the site reaches production scale though  it s more important that the code is organized and logical  than that it goes slightly faster

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This might help a PHP developer out  The below functions will strip white space  remove comments  and concatenate of all your CSS files  Then insert it into a  lt style gt  tag in the head before page load   The function below will strip comments and minify the passed in css  It is paired in conjunction with the next function    lt  php function minifyCSS  string           Minify CSS and strip comments        Strips Comments      string   preg replace             s       string        string   preg replace    n s  n     n    string          Minifies      string   preg replace     n r  t          string        string   preg replace              string        string   preg replace                     1   string          Remove semicolon      string   preg replace             string          Return Minified CSS     return  string      gt    You will call this function in the head of your document    lt  php function concatenateCSS  cssFiles           Load all relevant css files        concatenate all relevant css files      css           foreach   cssFiles as  cssFile                 css    css   file get contents   cssFile css                 minify all css      css   minifyCSS  css       echo   lt style gt  css lt  style gt        gt    Include the function concatenateCSS   in your document head  Pass in an array with the names of your stylesheets with its path IE  css styles css  You are not required to add the extension  css as it is added automatically in the function above    lt head gt       lt title gt  lt  title gt       lt  php      stylesheets   array           bootstrap css bootstrap min             css owl-carousel min             css style                 concatenateCSS   stylesheets          gt   lt  head gt

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One place where I use  import is when I m doing two versions of a page  English and French   I ll build out my page in English  using a main css   When I build out the French version  I ll link to a French stylesheet  main fr css    At the top of the French stylesheet  I ll import the main css  and then redefine specific rules for just the parts I need different in the French version

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I think the key in this are the two reasons why you are actually writing multiple CSS style sheets    You write multiple sheets because the different pages of your website require different CSS definitions  Or at least not all of them require all the CSS definitions one other pages require  So you split up the CSS files in order to optimize what sheets are load on the different pages and avoid loading too many CSS definitions  The second reason that comes to mind is that your CSS is getting that large that is becomes clumsy to handle and in order to make it easier to maintain the large CSS file you split them up into multiple CSS files    For the first reason the additional  lt link gt  tag would apply as this allows you to load different set of CSS files for different pages   For the second reason the  import statement appears as the most handy because you get multiple CSS files but the files loaded are always the same   From the perspective of the loading time there is no different  The browser has to check and download the seperated CSS files no matter how they are implemented

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I experienced a  high peak  of linked stylesheets you can add  While adding any number of linked Javascript wasn t a problem for my free host provider  after doubling number of external stylesheets I got a crash slow down  And the right code example is    import  stylesheetB css     So  I find it useful for having a good mental map  as Nitram mentioned  while still at hard-coding the design  Godspeed  And I pardon for English grammatical mistakes  if any

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Sometimes you have to use  import as opposed to inline    If you are working on a complex application that has 32 or more css files and you must support IE9 there is no choice   IE9 ignores any css file after the first 31 and this includes and inline  css   However  each sheet can import 31 others

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There is almost no reason to use  import as it loads every single imported CSS file separately and can slow your site down significantly  If you are interested in the optimal way to deal with CSS when it comes to page speed   this is how you should deal with all your CSS code    Open all your CSS files and copy the code of every single file  Paste all the code in between a single STYLE tag in the HTML header of your page Never use CSS  import or separate CSS files to deliver CSS unless you have a large amount of code or there is a specific need to    More detailed information here  http   www giftofspeed com optimize-css-delivery   The reason the above works best is because it creates less requests for the browser to deal with and it can immediately start rendering the CSS instead of downloading separate files

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They are very similar  Some may argue that  import is more maintainable  However  each  import will cost you a new HTTP request in the same fashion as using the  link  method  So in the context of speed it is no faster  And as  duskwuff  said  it doesn t load simultaneously which is a downfall

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From a page speed standpoint   import from a CSS file should almost never be used  as it can prevent stylesheets from being downloaded concurrently  For instance  if stylesheet A contains the text    import url  stylesheetB css      then the download of the second stylesheet may not start until the first stylesheet has been downloaded  If  on the other hand  both stylesheets are referenced in  lt link gt  elements in the main HTML page  both can be downloaded at the same time  If both stylesheets are always loaded together  it can also be helpful to simply combine them into a single file   There are occasionally situations where  import is appropriate  but they are generally the exception  not the rule

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There is not really much difference in adding a css stylesheet in the head versus using the import functionality  Using  import is generally used for chaining stylesheets so that one can be easily extended  It could be used to easily swap different color layouts for example in conjunction with some general css definitions  I would say the main advantage   purpose is extensibility   I agree with xbonez comment as well in that portability and maintainability are added benefits

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Nebo Iznad Mi  o Grgur  The following are all correct ways to use  import   import url  fineprint css   print   import url  bluish css   projection  tv   import  custom css    import url  chrome   communicator skin      import  common css  screen  projection   import url  landscape css   screen and  orientation landscape     source  https   developer mozilla org en-US docs Web CSS  import

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