css01 CSS Introduction

https://www.w3schools.com/css/css_intro.asp

 

CSS is the language we use to style a Web page.

What is CSS?

  • CSS stands for Cascading Style Sheets
  • CSS describes how HTML elements are to be displayed on screen, paper, or in other media
  • CSS saves a lot of work. It can control the layout of multiple web pages all at once
  • External stylesheets are stored in CSS files

CSS Demo - One HTML Page - Multiple Styles!

Here we will show one HTML page displayed with four different stylesheets. Click on the "Stylesheet 1", "Stylesheet 2", "Stylesheet 3", "Stylesheet 4" links below to see the different styles:

<html>

<head>
   <style>
      /* Stylesheet 1: */
      body {
         font: 100% Lucida Sans, Verdana;
         margin: 20px;
         line-height: 26px;
      }

      .container {
         xmin-width: 900px;
      }

      .wrapper {
         position: relative;
         overflow: auto;
      }

      #top,
      #sidebar,
      #bottom,
      .menuitem {
         border-radius: 4px;
         margin: 4px;
      }

      #top {
         background-color: #04AA6D;
         color: #ffffff;
         padding: 15px;
      }

      #menubar {
         width: 200px;
         float: left
      }

      #main {
         padding: 10px;
         margin: 0 210px;
      }

      #sidebar {
         background-color: #32a4e7;
         color: #ffffff;
         padding: 10px;
         width: 180px;
         bottom: 0;
         top: 0;
         right: 0;
         position: absolute;
      }

      #bottom {
         border: 1px solid #d4d4d4;
         background-color: #f1f1f1;
         text-align: center;
         padding: 10px;
         font-size: 70%;
         line-height: 14px;
      }

      #top h1,
      #top p,
      #menulist {
         margin: 0;
         padding: 0;
      }

      .menuitem {
         background-color: #f1f1f1;
         border: 1px solid #d4d4d4;
         list-style-type: none;
         padding: 2px;
         cursor: pointer;
      }

      .menuitem:hover {
         background-color: #ffffff;
      }

      .menuitem:first-child {
         background-color: #04AA6D;
         color: white;
         font-weight: bold;
      }

      a {
         color: #000000;
         text-decoration: underline;
      }

      a:hover {
         text-decoration: none;
      }


      @media (max-width: 800px) {
         #sidebar {
            width: auto;
            position: relative;
         }

         #main {
            margin-right: 0;
         }

      }

      @media (max-width: 600px) {
         #menubar {
            width: auto;
            float: none;
         }

         #main {
            margin: 0;
         }
      }
   </style>

   <style>
      /* Stylesheet 2: */
      body {
         font-family: Arial;
         background-color: #d14836;
         line-height: 20px;
      }

      .container {
         xmin-width: 900px;
      }

      .wrapper {
         position: relative;
         overflow: auto;
      }

      #top {
         color: #ffffff;
         padding: 15px;
         font-size: 30px;
         line-height: 26px;
      }

      #top h1 {
         margin: 0;
         line-height: 50px;
      }

      #menubar {
         width: 190px;
         float: right;
      }

      #main {
         padding: 10px;
         background-color: #ffffff;
         font: 80% Verdana;
      }

      #main h1,
      #main h2 {
         color: #d14836;
      }

      #sidebar {
         background-color: #F6DAD7;
         color: #d14836;
         padding: 10px;
      }

      #bottom {
         text-align: center;
         padding: 10px;
         font-size: 70%;
         color: #ffffff;
      }

      #menulist {
         padding: 0;
         font: 16px verdana;
      }

      .menuitem {
         width: 155px;
         background-color: #d14836;
         border: 1px solid #d14836;
         border-radius: 40px;
         color: #ffffff;
         list-style-type: none;
         margin: 10px;
         padding: 5px;
         text-align: center;
         cursor: pointer;
      }

      .menuitem:nth-child(2) {
         background-color: white;
         color: #d14836;
         font-weight: bold;
      }

      .menuitem:hover {
         background-color: #ffffff;
         color: #d14836;
      }

      a {
         color: #d14836;
         text-decoration: none;
      }

      a:hover {
         text-decoration: underline;
      }
   </style>

   <style>
      /* Stylesheet 3: */
      body {
         font: 100% Verdana;
         margin: 20px;
         line-height: 26px;
      }

      .container {
         xmin-width: 900px;
      }

      .wrapper {
         position: relative;
         overflow: auto;
      }

      #sidebar {
         background-color: #f1f1f1;
         border: 1px solid #d4d4d4;
         padding-left: 10px;
      }

      #bottom {
         text-align: center;
         padding: 10px;
         font-size: 70%;
         line-height: 14px;
      }

      h1,
      h2,
      h3 {
         color: #4CAF50;
      }

      #menulist {
         padding: 0;
         position: relative;
         overflow: auto;
      }

      .menuitem {
         width: 165px;
         float: left;
         background-color: #555555;
         color: #ffffff;
         list-style-type: none;
         margin: 4px;
         padding: 2px;
         text-align: center;
         cursor: pointer;
      }

      .menuitem:nth-child(3) {
         background-color: #04AA6D;
      }

      .menuitem:hover {
         background-color: #000;
      }

      a {
         color: #000000;
      }

      a:hover {
         color: #84c754;
      }
   </style>
   <style>
      /* Stylesheet 4: */
      body {
         font: 100% Courier New;
         margin: 20px;
         line-height: 26px;
         background-color: #000000;
      }

      .container {
         xmin-width: 900px;
      }

      .wrapper {
         position: relative;
         overflow: auto;
      }

      #top {
         color: #84c754;
         padding: 15px;
      }

      #main {
         padding: 10px;
         color: #84c754;
      }

      #sidebar {
         color: #ffffff;
         border: 1px solid #ffffff;
         border-radius: 4px;
         padding: 10px;
         width: 320px;
         top: 0;
         right: 0;
         position: absolute;
         font-size: 80%;
         line-height: 20px;
      }

      #bottom {
         border: 1px solid #ffffff;
         border-radius: 4px;
         color: #ffffff;
         text-align: center;
         padding: 10px;
         font-size: 70%;
         line-height: 14px;
      }

      #top h1,
      #top p {
         margin: 0;
      }

      .menuitem {
         color: #84c754;
         cursor: pointer;
      }

      .menuitem:nth-child(4) {
         color: white;
         font-weight: bold;
      }

      .menuitem:hover {
         color: #ffffff;
      }

      a {
         color: #ffffff;
      }

      a:hover {
         color: #84c754;
      }

      @media (max-width: 600px) {
         #sidebar {
            width: auto;
            margin-bottom: 10px;
            position: relative;
         }
      }
   </style>

</head>

<body>

   <div class="container wrapper">
      <div id="top">
         <h1>Welcome to My Homepage</h1>
         <p>Use the menu to select different Stylesheets</p>
      </div>
      <div class="wrapper">
         <div id="menubar">
            <ul id="menulist">
               <li class="menuitem" onclick="reStyle(0)">Stylesheet 1
               </li>
               <li class="menuitem" onclick="reStyle(1)">Stylesheet 2
               </li>
               <li class="menuitem" onclick="reStyle(2)">Stylesheet 3
               </li>
               <li class="menuitem" onclick="reStyle(3)">Stylesheet 4
               </li>
               <li class="menuitem" onclick="noStyles()">No Stylesheet
               </li>
            </ul>
         </div>
         <div id="main">
            <h1>Same Page Different Stylesheets</h1>
            <p>This is a demonstration of how different stylesheets can change the layout of your HTML page. You can
               change the layout of this page by selecting different stylesheets in the menu, or by selecting one of the
               following links:<br>
               <a href="#" onclick="reStyle(0);return false">Stylesheet1</a>,
               <a href="#" onclick="reStyle(1);return false">Stylesheet2</a>,
               <a href="#" onclick="reStyle(2);return false">Stylesheet3</a>,
               <a href="#" onclick="reStyle(3);return false">Stylesheet4</a>.
            </p>
            <h2>No Styles</h2>
            <p>This page uses DIV elements to group different sections of the HTML page. Click here to see how the page
               looks like with no stylesheet:<br><a href="#" onclick="noStyles();return false">No Stylesheet</a>.</p>
         </div>
         <div id="sidebar">
            <h3>Side-Bar</h3>
            <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut
               laoreet dolore magna aliquam erat volutpat.</p>
         </div>
      </div>


      <div id="bottom">
         Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet
         dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper
         suscipit lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure dolor in hendrerit in
         vulputate velit esse molestie consequat, vel illum dolore eu feugiat nulla facilisis at vero eros et accumsan
         et iusto odio dignissim qui blandit praesent luptatum zzril delenit augue duis dolore te feugait nulla
         facilisi.
      </div>
   </div>

   <script>
      function noStyles() {
         document.styleSheets[0].disabled = true;
         document.styleSheets[1].disabled = true;
         document.styleSheets[2].disabled = true;
         document.styleSheets[3].disabled = true;
      }

      function reStyle(n) {
         noStyles()
         document.styleSheets[n].disabled = false;
      }

      function closeBlackdiv() {
         var blackdiv, stylediv;
         blackdiv = document.getElementById("blackdiv")
         blackdiv.parentNode.removeChild(blackdiv);
         stylediv = document.getElementById("stylediv")
         stylediv.parentNode.removeChild(stylediv);
      }

      function showStyle(n) {
         var div, text, blackdiv;
         blackdiv = document.createElement("DIV");
         blackdiv.setAttribute("style", "background-color:#000000;position:absolute;width:100%;height:100%;top:0;opacity:0.5;margin-left:-20px;");
         blackdiv.setAttribute("id", "blackdiv");
         blackdiv.setAttribute("onclick", "closeBlackdiv()");
         document.body.appendChild(blackdiv);
         div = document.createElement("DIV");
         div.setAttribute("id", "stylediv");
         div.setAttribute("style", "background-color:#ffffff;padding-left:5px;position:absolute;width:auto;height:auto;top:100px;bottom:50px;left:200px;right:200px;overflow:auto;font-family: monospace; white-space: pre;line-height:16px;");
         text = document.createTextNode(document.getElementsByTagName("STYLE")[n].innerHTML);
         div.appendChild(text);
         document.body.appendChild(div);
         //alert(document.getElementsByTagName("STYLE")[n].innerHTML);
      }
      reStyle(0);
   </script>



</body>

</html>

 

 

 

Why Use CSS?

CSS is used to define styles for your web pages, including the design, layout and variations in display for different devices and screen sizes.

 

CSS Example

body {
  background-color: lightblue;
}

h1 {
  color: white;
  text-align: center;
}

p {
  font-family: verdana;
  font-size: 20px;
}

CSS Solved a Big Problem

HTML was NEVER intended to contain tags for formatting a web page!

HTML was created to describe the content of a web page, like:

<h1>This is a heading</h1>

<p>This is a paragraph.</p>

When tags like <font>, and color attributes were added to the HTML 3.2 specification, it started a nightmare for web developers. Development of large websites, where fonts and color information were added to every single page, became a long and expensive process.

To solve this problem, the World Wide Web Consortium (W3C) created CSS.

CSS removed the style formatting from the HTML page!

 

CSS Saves a Lot of Work!

The style definitions are normally saved in external .css files.

With an external stylesheet file, you can change the look of an entire website by changing just one file!

 

posted @ 2024-05-28 20:29  emanlee  阅读(7)  评论(0)  编辑  收藏  举报