合理CSS的核心原则，摘自CSS重构:从仅追加到模块化CSS

Write in SASS. You'd be insane to forego the advantages of variables, mixins, and so on. Never use an HTML ID for styling; always use classes. HTML IDs, when used correctly, appear only once in the whole page, which is the complete opposite of re-usability — one of the most basic goods in sensible engineering. Moreover, it's really hard to override selectors containing IDs and often the only way to overpower one HTML ID is to create another ID, causing IDs to propagate in the codebase like the pests they are. Better to leave the HTML IDs for unchanging Javascript or integration test hooks. Name your CSS classes by their visual function rather than by their application-specific function. For example, say ".highlight-box" instead of ".bundle-product-discount-box". Coding in this way means that you can re-use your existing style-sheets when you role out side-businesses. For example, we started out selling law notes but recently moved into law tutors. Our old CSS classes had names like ".download_document_box", a class name that makes sense when talking about digital documents but would only confuse when applied to the new domain of private tutors. A better name that fits both existing services — and any future ones — would be ".pretty_callout_box". Avoid naming CSS classes after specific grid information. There was (and still is) a dreadful anti-pattern in CSS communities whereby designers and creators of CSS frameworks (cough Twitter Bootstrap) believe that "span-2" or "cols-8" are reasonable names for CSS classes. The point of CSS is to give you the possibility to modify your design without affecting the markup (much). Hardcoding grids sizes into the HTML thwarts this goal, so it is advised against in any project expected to last longer than a weekend. More on how we avoided grid classes later. Split your CSS across files. Ideally you would split everything into "components"/"widgets" and then compose pages from these atoms of design. Realistically though, you'll notice that some of your website pages have idiosyncrasies (e.g. a special layout, or a weird photo gallery that appears in just one article). In these cases you might create a file related to that specific page, only refactoring into a full-blown widget when it becomes clear that the element will be re-used elsewhere. This is a tradeoff, one that is motivated by practical budgetary concerns. Minimise nesting. Introduce new classes instead of nesting selectors. The fact that SASS removes the pain of repeating selectors when nesting doesn't mean that you have to nest five levels deep. Never over-qualify a selector (e.g. don't use "ul.nav" where ".nav" could do the same job.) And don't specify HTML elements alongside the custom class name (e.g."h2.highlight"). Instead just use the class name alone and drop the base selector (e.g. the previous example should be ".highlight"). Over-qualifying selectors doesn't add any value. Create styles for HTML elements (e.g. "h1") only when styling base components which should be consistent in the whole application. Avoid broad selectors like "header ul" because it's likely that you have to override them in some places anyway. As we keep saying, most of the time you want to use a specific, well-named class whenever you want a particular style. Embrace the basics of Block-Element-Modifier. You can read about it for example on here. We used it quite lightly, but still it helped us a lot in organising CSS styles.

很多时候，我看到有人把文件分成几个部分，在部分之间加上标题注释。

类似的

/* Headings and General Text */

.... stuff here for H1, etc..

/* Main page layout */

.... stuff here for layout page setup etc.

它工作得很好，可以让你很容易回头看看你正在做什么。

你应该看看边界元法。

理论

BEM试图提供一组用于组织和命名css选择器的指令，以使选择器更具可重用性和模块化，并避免选择器之间的冲突，这种冲突通常会导致意大利面条式的代码和特定的问题。

如果正确使用，它实际上有一些非常积极的影响。

当样式被添加到元素中时，它们的作用是您所期望的 样式不会泄露，并且只影响它们所添加的内容 样式与文档结构完全解耦 不同的风格不需要被强迫凌驾于彼此之上

BEM works well with SASS to bring an almost object oriented style to CSS. You can build modular files, that handle the display of a single UI element and contain variables, such as colours and 'methods' such as how internal elements are handled. While a hardcore OO programmer might balk at this idea, in fact, the applied concepts bring in a lot of the nicer parts of OO structures, such as modularity, loose coupling and tight cohesion and context free re-usability. You can even build in a way that looks like an encapsulated object by using Sass and the & operator.

更多来自Smashing杂志的深入文章可以在这里找到;还有一个来自CCS Wizardry的Harry Roberts(任何参与css的人都应该读一下他的书)。

在实践中

我已经用过它几次了，还用过SMACSS和OOCSS，这意味着我也可以对它们进行比较。我也在一些大混乱中工作过，通常是我自己没有经验的创作。

当我在现实世界中使用BEM时，我用一些额外的原则来增强这种技术。我利用实用工具类-一个很好的例子是包装类:

.page-section {
    width: 100%;
}
@media screen and (min-width: 1200px) {
    margin: 0 auto;
    width: 1200px;
}

我也有些依赖于级联和特异性。在这里，BEM模块将是.primary-box，而.header将是特定重写的上下文

.header {
  .primary-box {
    color: #000;
  }
}

(我尽我最大的努力使所有的东西都是通用的和上下文无关的，这意味着一个好的项目几乎所有的东西都在可重用的模块中)

我想说的最后一点是，无论你的项目看起来多么小，多么简单，你都应该从一开始就这么做，原因有二:

项目越来越复杂，所以打下良好的基础是很重要的，包括CSS 即使是一个看起来很简单的项目，因为它是建立在WordPress上的，JavaScript很少，但在CSS中仍然非常复杂——好吧，你不需要做任何服务器端编码，所以这部分很简单，但是宣传册前端有20个模块和每个模块的3个变体:你有一些非常复杂的CSS !

Web组件

在2015年，我们开始关注Web组件。我对这些还不太了解，但它们希望将所有前端功能放在自包含的模块中，有效地尝试将各种原则从BEM应用到前端作为一个整体，并将分散但完全耦合的元素(如DOM片段、Js (MVC)和CSS)组合在一起，这些元素都构建相同的UI小部件。

通过这样做，他们b将解决css中存在的一些原始问题，我们试图用BEM等东西来解决这些问题，同时使其他一些前端架构更加合理。

这里有一些进一步的阅读材料，还有一个框架聚合物，非常值得一看

最后

我也认为这是一个优秀的、现代的css最佳实践指南——专门为防止大型css项目变得混乱而设计。我尽量遵循其中的大部分。

我已经使用级联样式表(CSS)超过20年了。所以下面是我的解决方案来帮助你:

ALWAYS use External CSS via a <link> tag. External CSS is far superior to "embedded" <style> and "inline" element styles <span style="color:blue;">my text</span> simply because external styles downloaded to the browser are cached for every page in your website and affect all web pages, not just one. Consider moving all those styles sprinkled throughout your website to CSS classes in your sheets. Make sure you add selectors to increase their weight in cases where they might have cascaded over earlier inherited styles. Note: Many JavaScript API's like Angular and others use embedded CSS which means they are slower and have to reload CSS every refresh or revisit to the site. Bad design! ALWAYS use a "Reset" Style Sheet for all your basic HTML Elements. Most CSS packages like Bootstrap and others come with a reset or reboot sheet. These restyle all your HTML element selectors so they look decent across all browsers and user agents. This saves you the nightmare of having to restyle and customize design across basic elements like form controls, layouts, text, etc. I wrote my own "reset" sheet years ago. I am going to post it on GitHub under "Universal CSS Framework" soon if you would like mine. Works in all the old and new browsers. Remember, all text-based styles cascade and inherit naturally down through the sites elements! So, you should rarely need to repeat font styles, line-heights, etc. Most young developers forget this. Text-based styles are inherited down the HTML tree so only have to be written one time in a parent. Often the <body> element is the best placed to set basic font styles, etc. Because of #3 you do NOT need CSS precrocessors like SASS to reorganize or manage your style sheets. Stay away from these third-party dependencies. CSS can be written to inherit or cascade styles through the site so you do not have to repeat the same font styling or properties across CSS classes, etc. Group your Block Level/Layout styles that control design. Use ID selectors (#myid) on top level HTML blocks to separate sections and use those in CSS selectors to manage items specific to that page or website section (#main .someclass {...}). These have the advantage that they are easy to track and easy to segregate, but ID selectors have very high selectivity or weight. ID selectors have a 1-0-0 or 100 weight over class which has 0-1-0 or 10 weight. This prevents any later style shifts from damaging your previous custom styles in specific protected sections. Design all CSS around a Single CSS Class that can be Reused. Avoid attaching more element and chains of classes in CSS selectors until you absolutely need to override a common shared class with a custom one. Example: .articlelink{...} would be the shared universal style everyone can access. .block1 .area2 .articlelink{...} would allow you to create a custom version throughout a section without creating a new class or changing the HTML. Use CSS Comments! /* My New Styles */ ...followed by blocks of related CSS or just use comments to explain what is not intuitive in your code. If you have big projects, have each developer write their own custom CSS sheets for their sections, but inherit the main site style sheets. First, make sure all sections of the website link to your basic reset and base site sheets first. This allows basic element styles, font settings, layout, page design, forms, and colors to be enforced by the base sheets first so developers only add new styles needed rather than reinventing the same wheel. As you update the base sheets all developers inherit, those appear naturally across all sections of the project with no effort, and the teams can see those instantly.

Remember, you are working with cascading style sheets, not style sheets! That means most text-based styles are designed to inherit from all the parent elements, then cascade those same styles down into your trees of HTML across thousands of pages with no extra code. Most new web developers fail to grasp the simplicity of CSS, so struggle with SASS and other tools to fix it. It just is not needed. CSS was designed this way over 20 years ago by very smart people that solved all these issues for you.

如果你真的开始以正确的方式使用CSS，你会发现你可以删除大部分样式，SASS，最小化，以及其他外部例程和你的网站曾经使用过的额外代码，同时享受CSS的级联效果，这些效果在很久以前就被设计为使最小代码成为可能。

<html>
  <body style="color:blue;">
    <main>
      <section>
        <div>
          <div>
            <div>
              <p>hello blue world</p>
            </div>
          </div>
        </div>
      </section>
    </main>
  </body>
</html>

和平

以下是4个例子:

CSS约定/代码布局模型 在编写我的第一个样式表时，我应该遵循哪些CSS标准? 整理CSS的最佳方法是什么? 最佳实践- CSS样式表格式

在所有4个问题上，我的回答都包含了下载并阅读Natalie Downe的PDF CSS系统的建议。(PDF包含了大量幻灯片上没有的注释，所以请阅读PDF!)注意她对组织的建议。

四年后，我想说:

Use a CSS pre-processor and manage your files as partials (I personally prefer Sass with Compass, but Less is quite good as well and there are others) Read up on concepts like OOCSS, SMACSS, and BEM or getbem. Take a look at how popular CSS frameworks like Bootstrap and Zurb Foundation are structured. And don't discount less popular frameworks - Inuit is an interesting one but there are plenty others. Combine/minify your files with a build step on a continuous integration server and/or a task runner like Grunt or Gulp.

我可以建议少CSS动态框架吗

它类似于前面提到的SASS。

它帮助维护每个父类的CSS。

E.g.

 #parent{     
  width: 100%;

    #child1
    {    
     background: #E1E8F2;    
     padding: 5px;    
    }

    #child2
   {
     background: #F1F8E2;
     padding: 15px
   }
 }

它的作用: 将width:100%应用于#child1和#child2。

此外，#child1特定的CSS属于#parent。

这将导致

#parent #child1
{
 width: 100%;
 background: #E1E8F2;
 padding: 5px;
}

#parent #child2
{
 width: 100%;
 background: #F1F8E2;
 padding: 15px;
}