您还应该了解级联、权重以及它们是如何工作的。

我注意到您只使用了类标识符(div.title)。您知道您也可以使用ID，而且ID比类更重要吗?

例如,

#page1 div.title, #page1 ul, #page1 span {
  // rules
}

将使所有这些元素共享一个字体大小，或者颜色，或者任何你的规则。您甚至可以使所有的div都是#page1的后代获得某些规则。

至于重量，请记住CSS轴从最一般/最轻到最特定/最重。也就是说，在CSS选择器中，一个元素说明符被一个类说明符取代，一个ID说明符取代。数字计数，因此具有两个元素说明符(ul li)的选择器将比只有一个说明符(li)的选择器具有更大的权重。

把它想象成数字。个位上的9仍然小于十位上的1。一个有ID说明符、一个类说明符和两个元素说明符的选择器，将比没有ID、500个类说明符和1000个元素说明符的选择器具有更大的权重。当然，这是一个荒谬的例子，但你可以理解。关键是，应用这个概念可以帮助您清理大量CSS。

顺便说一句，在类中添加元素说明符(div.title)是没有必要的，除非你遇到了与其他具有class="title"的元素冲突。不要增加不必要的重量，因为你以后可能会用到这些重量。

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;
}

这是一个非常好的问题。在我所看到的任何地方，CSS文件都倾向于在一段时间后失去控制——尤其是，但不仅仅是在团队中工作时。

以下是我自己努力遵守的规则(并不是说我总能做到)。

Refactor early, refactor often. Frequently clean up CSS files, fuse together multiple definitions of the same class. Remove obsolete definitions immediately. When adding CSS during fixing bugs, leave a comment as to what the change does ("This is to make sure the box is left aligned in IE < 7") Avoid redundancies, e.g. defining the same thing in .classname and .classname:hover. Use comments /** Head **/ to build a clear structure. Use a prettifier tool that helps maintain a constant style. I use Polystyle, with which I'm quite happy (costs $15 but is money well spent). There are free ones around as well (e.g. Code Beautifier based on CSS Tidy, an open-source tool). Build sensible classes. See below for a few notes on this. Use semantics, avoid DIV soup - use <ul>s for menus, for example. Define everything on as low a level as possible (e.g. a default font family, colour and size in the body) and use inherit where possible If you have very complex CSS, maybe a CSS pre-compiler helps. I'm planning to look into xCSS for the very same reason soon. There are several others around. If working in a team, highlight the necessity of quality and standards for CSS files as well. Everybody's big on coding standards in their programming language(s), but there is little awareness that this is necessary for CSS too. If working in a team, do consider using Version Control. It makes things that much easier to track, and editing conflicts that much easier to solve. It's really worth it, even if you're "just" into HTML and CSS. Do not work with !important. Not only because IE =< 7 can't deal with it. In a complex structure, the use of !important is often tempting to change a behaviour whose source can't be found, but it's poison for long-term maintenance.

构建合理的类

这就是我喜欢构建合理类的方式。

我首先应用全局设置:

body { font-family: .... font-size ... color ... }
a { text-decoration: none; }

然后，我确定页面布局的主要部分。顶部区域、菜单、内容和页脚。如果我写了好的标记，这些区域将与HTML结构相同。

然后，我开始构建CSS类，在合理的情况下指定尽可能多的祖先，并将相关类尽可能紧密地分组。

div.content ul.table_of_contents 
div.content ul.table_of_contents li 
div.content ul.table_of_contents li h1
div.content ul.table_of_contents li h2
div.content ul.table_of_contents li span.pagenumber

你可以把整个CSS结构想象成一棵树，它的定义越远越具体。你想要尽可能地减少课程的数量，并且尽可能少地重复学习。

例如，假设您有三个级别的导航菜单。 这三个菜单看起来不同，但它们也有一些共同的特征。例如，它们都是<ul>，它们都有相同的字体大小，并且项目都是彼此相邻的(与ul的默认呈现相反)。此外，所有菜单都没有项目符号(list-style-type)。

首先，在一个名为menu的类中定义公共特征:

div.navi ul.menu { display: ...; list-style-type: none; list-style-image: none; }
div.navi ul.menu li { float: left }

然后，定义这三个菜单的具体特征。第1级是40像素高;2级和3级，20像素。

注意:您也可以为此使用多个类，但Internet Explorer 6在使用多个类时存在问题，因此本例使用id。

div.navi ul.menu#level1 { height: 40px; }
div.navi ul.menu#level2 { height: 20px; }
div.navi ul.menu#level3 { height: 16px; }

菜单的标记看起来像这样:

<ul id="level1" class="menu"><li> ...... </li></ul>
<ul id="level2" class="menu"><li> ...... </li></ul>
<ul id="level3" class="menu"><li> ...... </li></ul>

如果页面上有语义相似的元素(比如这三个菜单)，首先试着找出共性，然后把它们放到一个类中;然后，计算出特定的属性并将它们应用到类中，或者，如果您必须支持Internet Explorer 6，则应用ID。

其他HTML技巧

如果你将这些语义添加到HTML输出中，设计师以后可以使用纯CSS定制网站和/或应用程序的外观，这是一个很大的优势和节省时间。

If possible, give every page's body a unique class: <body class='contactpage'> this makes it very easy to add page-specific tweaks to the style sheet: body.contactpage div.container ul.mainmenu li { color: green } When building menus automatically, add as much CSS context as possible to allow extensive styling later. For example: <ul class="mainmenu"> <li class="item_first item_active item_1"> First item </li> <li class="item_2"> Second item </li> <li class="item_3"> Third item </li> <li class="item_last item_4"> Fourth item </li> </ul> This way, every menu item can be accessed for styling according to its semantic context: Whether it's the first or last item in the list; Whether it's the currently active item; and by number.

请注意，如上例中所述的多个类的分配在IE6中不能正常工作。有一个变通方案可以使IE6能够处理多个类。如果没有解决方法，则必须设置对您来说最重要的类(项目编号、活动或第一个/最后一个)，或者使用id。

我建议你看看“指南针风格”CSS框架。

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.

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。