Challenge solutions - Developer guides 编辑

This page provides solutions to the challenges posed in the CSS Getting Started tutorial. These are not the only possible solutions. The sections below correspond to the titles of the tutorial sections.

Why use CSS

Colors

Challenge

Without looking up a reference, find five more color names that work in your stylesheet.

Solution

CSS supports common color names like orange, yellow, blue, green, or black. It also supports some more exotic color names like chartreuse, fuschia, or burlywood. See CSS Color value for a complete list as well as other ways of specifying colors.

How CSS works

DOM inspector

Challenge

In DOMi, click on a STRONG node. Use DOMi's right-hand pane to find out where the node's color is set to red, and where its appearance is made bolder than normal text.

Solution

In the menu above the right-hand pane, choose CSS Rules.  You see two items listed, one that references an internal resource and one that references your stylesheet file. The internal resource defines the font-weight property as bolder; your stylesheet defines the color property as red.

Cascading and inheritance

Inherited styles

Challenge

Change your stylesheet so that only the red letters are underlined.

Solution

Move the declaration for underlining from the rule for <p> to the one for <strong>. The resulting file looks like this:

p {color: blue; }
strong {color: orange; text-decoration: underline;}

Later sections of this tutorial describe style rules and declarations in greater detail.

Selectors

Second paragraph blue

Challenge

Without changing your HTML file, add a single rule to your CSS file that keeps all the initial letters the same color as they are now, but makes all the other text in the second paragraph blue.

Solution

Add a rule with an ID selector of #second and a declaration color: blue;, as shown below:

#second { color: blue; }

A more specific selector, p#second also works.

Both paragraphs blue

Challenge

Now change the rule you have just added (without changing anything else), to make the first paragraph blue too.

Solution

Change the selector of the new rule to be a tag selector using p:

p { color: blue; }

The rules for the other colors all have more specific selectors, so they override the blue of the paragraph.

Readable CSS

Commenting out a rule

Challenge

Comment out part of your stylesheet, without changing anything else, to make the very first letter of your document red.

Solution

One way to do this is to put comment delimiters around the rule for .carrot:

/*
.carrot {
  color: orange;
}
*/

Text styles

Big initial letters

Challenge

Without changing anything else, make all six initial letters twice the size in the browser's default serif font.

Solution

Add the following style declaration to the strong rule:

  font: 200% serif;

If you use separate declarations for font-size and font-family, then the font-style setting on the first paragraph is not overridden.

Color

Three-digit color codes

Challenge

In your CSS file, change all the color names to 3-digit color codes without affecting the result.

Solution

The following values are reasonable approximations of the named colors:

strong {
  color: #f00; /* red */
  background-color: #ddf; /* pale blue */
  font: 200% serif;
}

.carrot {
  color: #fa0; /* orange */
}

.spinach {
  color: #080; /* dark green */
}

p {
  color: #00f; /* blue */
}

Content

Add an image

Challenge

Add a one rule to your stylesheet so that it displays the image at the start of each line.

Solution

Add this rule to your stylesheet:

p:before{
  content: url("yellow-pin.png");
}

Lists

Lower Roman numerals

Challenge

Add a rule to your stylesheet, to number the oceans using Roman numerals from i to v.

Solution

Define a rule for list items to use the lower-roman list style:

li {
  list-style: lower-roman;
}

Capital letters

Challenge

Change your stylesheet to identify the headings with capital letters in parentheses.

Solution

Add a rule to the body element (parent of the headings) to reset a new counter, and one to display and increment the counter on the headings:

/* numbered headings */
body {counter-reset: headnum;}
h3:before {
  content: "(" counter(headnum, upper-latin) ") ";
  counter-increment: headnum;
}

Boxes

Ocean border

Challenge

Add one rule to your stylesheet, making a wide border all around the oceans in a color that reminds you of the sea.

Solution

The following rule achieves this effect:

ul {
  border: 10px solid lightblue;
  width:  100px;
}

Layout

Default image position

Fixed image position

Challenge

Change your sample document, doc2.html, adding this tag to it near the end, just before </BODY>: <IMG id="fixed-pin" src="Yellow-pin.png" alt="Yellow map pin"> Predict where the image will appear in your document. Then refresh your browser to see if you were correct.

Solution

The image appears to the right of the second list.

Challenge

Add a rule to your stylesheet that places the image in the top right of your document.

Solution

The following rule achieves the desired result:

#fixed-pin  {
  position:fixed;
  top: 3px;
  right: 3px;
} 

Tables

Borders on data cells only

Challenge

Change the stylesheet to make the table have a green border around only the data cells.

Solution

The following rule puts borders around only <td> elements that are inside the <tbody> element of the table with id=demo-table:

#demo-table tbody td {
  border:1px solid #7a7;
}

Media

Separate print style file

Challenge

Move the print-specific style rules to a separate CSS file and import them into your style4.css stylesheet.

Solution

Cut and paste the lines between /* print only */ and /* end print only */ into a file named style4_print.css. In style4.css, add the following line at the beginning of the file:

@import url("style4_print.css") print;

Heading hover color

Challenge

Make the headings turn blue when the mouse pointer is over them.

Solution

The following rule achieves the desired result:

h1:hover {
  color: blue;
}

JavaScript

Move box to the right

Challenge

Change the script so that the square jumps to the right by 20 em when its color changes, and jumps back afterwards.

Solution

Add lines to modify the margin-left property. Be sure to specify it as marginLeft in JavaScript. The following script achieves the desired result:

// JavaScript demonstration
function doDemo (button) {
  var square = document.getElementById("square");
  square.style.backgroundColor = "#fa4";
  square.style.marginLeft = "20em";
  button.setAttribute("disabled", "true");
  setTimeout(clearDemo, 2000, button);
}

function clearDemo (button) {
  var square = document.getElementById("square");
  square.style.backgroundColor = "transparent";
  square.style.marginLeft = "0em";
  button.removeAttribute("disabled");
}

SVG and CSS

Change color of inner petals

Challenge

Change the stylesheet so that the inner petals all turn pink when the mouse pointer is over any one of them, without changing the way the outer petals work.

Solution

Move the position of the :hover pseudo-class from a specific petal, to all petals

#inner-petals {
  --segment-fill-fill-hover: pink;
}

/* Non-standard way for some older browsers */
#inner-petals:hover .segment-fill {
  fill: pink;
  stroke: none;
}