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Cascading Style Sheets简介

Cascading Style Sheets,缩写为CSS,指层叠样式表。它是一种用于描述HTML或XML(或其他SGML衍生语言)文档如何呈现在屏幕、纸张或其他介质上的样式语言。CSS的发展是为了解决内容与表现分离的问题,它使得页面的结构化与表现性分离开来,简化结构,同时提高页面的展示效果。

一、CSS的基本语法

<style>
    选择器 {
        属性1: 值1;
        属性2: 值2;
        ...
    }
    选择器 {
        属性1: 值1;
        属性2: 值2;
        ...
    }
</style>

CSS的选择器决定了CSS定义的样式应用到哪些HTML元素上。CSS的选择器可以基于元素名称、ID、类名等属性进行选择。一般情况下,将CSS样式定义在<head>中的<style>标签中或者外部CSS文件中保存。

示例代码如下:

<!DOCTYPE html>
<html>
<head>
    <title>CSS基本语法示例</title>
    <style>
        h1 {
            font-size: 32px;
            color: #333;
            text-align: center;
        }
        .content {
            font-size: 18px;
            color: #666;
            line-height: 1.5;
        }
    </style>
</head>
<body>
    <h1>欢迎光临本站</h1>
    <p class="content">CSS,缩写为Cascading Style Sheets,指层叠样式表。它是一种用于描述HTML或XML文档如何呈现在屏幕、纸张或其他介质上的样式语言。</p>
</body>
</html>

二、CSS的优势

1. 提高页面的展示效果
CSS可以控制页面的各种样式,包括字体、颜色、边框、背景等。通过使用CSS,我们可以使页面更加美观、易读、易用。

2. 简化结构
通过CSS的样式定义,我们可以将HTML文档的结构化设计与样式表现分离开来。这样,不仅减少了HTML文件中的冗余代码,而且减少了代码的重复性,提高了网页的维护效率。

3. 提高搜索引擎优化
搜索引擎可以更好地抓取网页的内容和结构,避免了抓取样式代码所带来的干扰。而且,CSS的分离还可以减少HTML代码量,提高网页的速度,从而提高搜索引擎优化。

三、CSS的应用场景

1. 网页设计
CSS的核心作用是设计网页样式,网页的结构和布局都是通过HTML标签和CSS样式定义来实现的。CSS可以帮助我们设计出美观、易读、易用的网页,而且减少了HTML文件的代码量,降低了网页的维护成本。

2. 移动开发
目前,移动设备的使用越来越普遍,而且移动设备的屏幕大小、屏幕分辨率等都不尽相同,因此需要使用CSS来适配各种不同的移动设备。通过CSS的媒体查询,我们可以为不同的设备设置不同的样式,从而适应不同的设备。

3. 响应式网页设计
响应式网页设计是指通过CSS的技术实现网站的自适应,使得网站能够适应不同大小的屏幕和设备。响应式网页设计是一种趋势,为用户带来更好的用户体验。在响应式网页设计中,我们需要使用CSS的布局技术和媒体查询技术来实现自适应。

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when-present<#else>when-missing. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)?? ---- ---- FTL stack trace ("~" means nesting-related): - Failed at: ${item.id} [in template "article/detail/index.ftl" at line 48, column 106] ---- Java stack trace (for programmers): ---- freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...] at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134) at freemarker.core.EvalUtil.coerceModelToTextualCommon(EvalUtil.java:481) at freemarker.core.EvalUtil.coerceModelToStringOrMarkup(EvalUtil.java:401) at freemarker.core.EvalUtil.coerceModelToStringOrMarkup(EvalUtil.java:370) at freemarker.core.DollarVariable.calculateInterpolatedStringOrMarkup(DollarVariable.java:104) at freemarker.core.DollarVariable.accept(DollarVariable.java:63) at freemarker.core.Environment.visit(Environment.java:371) at freemarker.core.IteratorBlock$IterationContext.executedNestedContentForCollOrSeqListing(IteratorBlock.java:321) at freemarker.core.IteratorBlock$IterationContext.executeNestedContent(IteratorBlock.java:271) at freemarker.core.IteratorBlock$IterationContext.accept(IteratorBlock.java:244) at freemarker.core.Environment.visitIteratorBlock(Environment.java:645) at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:108) at freemarker.core.IteratorBlock.accept(IteratorBlock.java:94) at freemarker.core.Environment.visit(Environment.java:335) at freemarker.core.Environment.visit(Environment.java:341) at freemarker.core.Environment.visit(Environment.java:341) at freemarker.core.Environment.process(Environment.java:314) at freemarker.template.Template.process(Template.java:383) at org.springframework.web.servlet.view.freemarker.FreeMarkerView.processTemplate(FreeMarkerView.java:332) at org.springframework.web.servlet.view.freemarker.FreeMarkerView.doRender(FreeMarkerView.java:266) at org.springframework.web.servlet.view.freemarker.FreeMarkerView.renderMergedTemplateModel(FreeMarkerView.java:220) at org.springframework.web.servlet.view.AbstractTemplateView.renderMergedOutputModel(AbstractTemplateView.java:181) at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:314) at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1431) at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1167) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1106) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at com.software.filter.HttpSpiderIdentifyFilter.doFilter(HttpSpiderIdentifyFilter.java:51) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:340) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) at java.base/java.lang.VirtualThread.run(VirtualThread.java:309)