CSS Pseudo-classes: The Magic of Element States ✨

Welcome to Professor McGonagall's Transfiguration class! Today, we'll master CSS Pseudo-classes - the magical art of styling elements based on their state or position. Just like a wizard's spell can change based on circumstances, elements can change their appearance based on different states! 🧙‍♂️

Understanding Pseudo-classes 📚

User Action Pseudo-classes 🖱️

How do elements respond to user interactions?

Like a magical object responding to touch, these pseudo-classes react to user actions.

.magical-button {
    background: #540099;
    color: white;
    transition: all 0.3s ease;
    
    /* Mouse hover */
    &:hover {
        background: #6600cc;
        transform: translateY(-2px);
    }
    
    /* Active state (clicking) */
    &:active {
        transform: translateY(1px);
    }
    
    /* Focus state (keyboard navigation) */
    &:focus {
        outline: 3px solid rgba(84, 0, 153, 0.5);
        outline-offset: 2px;
    }
    
    /* Focus within (container) */
    &:focus-within {
        background: #f0e6ff;
    }
}

Form State Pseudo-classes 📝

How do we style form elements based on their state?

Like a potion changing colors based on its ingredients, form elements can change based on their state.

.magical-input {
    border: 2px solid #ccc;
    transition: all 0.3s ease;
    
    /* When input has content */
    &:not(:placeholder-shown) {
        border-color: #540099;
    }
    
    /* Valid input state */
    &:valid {
        border-color: #00994d;
        background: rgba(0, 153, 77, 0.1);
    }
    
    /* Invalid input state */
    &:invalid {
        border-color: #cc0000;
        background: rgba(204, 0, 0, 0.1);
    }
    
    /* Disabled state */
    &:disabled {
        background: #f5f5f5;
        cursor: not-allowed;
        opacity: 0.7;
    }
    
    /* Required fields */
    &:required {
        border-left-width: 4px;
    }
    
    /* Read-only state */
    &:read-only {
        background: #f8f8f8;
        cursor: default;
    }
    
    /* Optional fields */
    &:optional {
        border-style: dashed;
    }
}

Structural Pseudo-classes 🏗️

How do we select elements based on their position?

Like selecting specific students in a line, these pseudo-classes target elements based on their position.

.spell-list {
    /* First child */
    li:first-child {
        font-weight: bold;
        border-top: none;
    }
    
    /* Last child */
    li:last-child {
        border-bottom: none;
    }
    
    /* Specific position */
    li:nth-child(3) {
        color: #540099;
    }
    
    /* Every other item */
    li:nth-child(odd) {
        background: rgba(84, 0, 153, 0.1);
    }
    
    /* Every third item */
    li:nth-child(3n) {
        margin-bottom: 2em;
    }
    
    /* First of type */
    p:first-of-type {
        font-size: 1.2em;
    }
    
    /* Empty elements */
    li:empty {
        display: none;
    }
}

Link State Pseudo-classes 🔗

How do we style links in different states?

Like a magic portal changing colors as you use it, links can have different states.

.magical-link {
    /* Unvisited link */
    &:link {
        color: #540099;
        text-decoration: none;
    }
    
    /* Visited link */
    &:visited {
        color: #800080;
    }
    
    /* Mouse over link */
    &:hover {
        color: #6600cc;
        text-decoration: underline;
    }
    
    /* Active (clicking) link */
    &:active {
        color: #cc00ff;
    }
}

Advanced Selectors 🎯

Combining Pseudo-classes

Complex State Selection

.magical-form {
    /* Valid input that's not empty */
    input:valid:not(:placeholder-shown) {
        border-color: green;
    }
    
    /* First required input */
    input:required:first-of-type {
        border-left: 4px solid red;
    }
    
    /* Hover state on enabled buttons */
    button:enabled:hover {
        transform: scale(1.05);
    }
}

Negation Pseudo-class (:not)

Excluding Elements

.spell-list {
    /* All items except the last */
    li:not(:last-child) {
        border-bottom: 1px solid #eee;
    }
    
    /* All inputs except disabled ones */
    input:not(:disabled) {
        background: white;
    }
    
    /* Everything except certain classes */
    *:not(.exclude):not(.another-exclude) {
        margin-bottom: 1rem;
    }
}

Common Patterns 📝

1. Interactive Cards

Card Interactions

.magical-card {
    transition: all 0.3s ease;
    
    /* Hover effects */
    &:hover {
        transform: translateY(-5px);
        box-shadow: 0 5px 15px rgba(0,0,0,0.2);
    }
    
    /* Focus for accessibility */
    &:focus-within {
        outline: 3px solid #540099;
        outline-offset: 2px;
    }
    
    /* Disabled state */
    &.disabled {
        opacity: 0.7;
        
        &:hover {
            transform: none;
            box-shadow: none;
        }
    }
}

2. Form Validation

Form States

.magical-form {
    /* Label states */
    label {
        &:has(+ input:required)::after {
            content: "*";
            color: red;
        }
        
        &:has(+ input:valid) {
            color: green;
        }
    }
    
    /* Input states */
    .input-group {
        position: relative;
        
        input {
            border: 2px solid #ccc;
            
            &:focus {
                border-color: #540099;
                outline: none;
            }
            
            &:valid:not(:placeholder-shown) {
                border-color: green;
                
                & + .validation-icon::before {
                    content: "✓";
                    color: green;
                }
            }
            
            &:invalid:not(:placeholder-shown) {
                border-color: red;
                
                & + .validation-icon::before {
                    content: "✕";
                    color: red;
                }
            }
        }
    }
}

3. Navigation Menus

Navigation States

.magical-nav {
    /* Current page */
    .nav-link:is(.active, [aria-current="page"]) {
        color: #540099;
        font-weight: bold;
    }
    
    /* Dropdown behavior */
    .dropdown {
        display: none;
        
        .nav-item:hover > & {
            display: block;
        }
    }
    
    /* Mobile states */
    @media (max-width: 768px) {
        .nav-item:not(:last-child) {
            border-bottom: 1px solid #eee;
        }
    }
}

Practical Tasks 📚

Task 1: Create an Interactive Form

Task

Create a form with comprehensive state styling:

• Input states (focus, valid, invalid)
• Required fields
• Disabled states
• Custom checkboxes and radio buttons

Answer

.magical-form {
    /* Form layout */
    display: grid;
    gap: 1.5rem;
    
    /* Form groups */
    .form-group {
        position: relative;
        
        /* Labels */
        label {
            display: block;
            margin-bottom: 0.5rem;
            color: #333;
            
            &:has(+ input:required)::after {
                content: "*";
                color: #cc0000;
                margin-left: 0.25rem;
            }
        }
        
        /* Inputs */
        input:not([type="checkbox"], [type="radio"]) {
            width: 100%;
            padding: 0.75rem;
            border: 2px solid #ccc;
            border-radius: 4px;
            transition: all 0.3s ease;
            
            &:hover:not(:disabled) {
                border-color: #666;
            }
            
            &:focus {
                outline: none;
                border-color: #540099;
                box-shadow: 0 0 0 3px rgba(84, 0, 153, 0.2);
            }
            
            &:valid:not(:placeholder-shown) {
                border-color: #00994d;
                
                & ~ .validation-icon::before {
                    content: "✓";
                    color: #00994d;
                }
            }
            
            &:invalid:not(:placeholder-shown) {
                border-color: #cc0000;
                
                & ~ .validation-icon::before {
                    content: "✕";
                    color: #cc0000;
                }
            }
            
            &:disabled {
                background: #f5f5f5;
                cursor: not-allowed;
                opacity: 0.7;
            }
        }
        
        /* Custom checkbox */
        .checkbox-wrapper {
            position: relative;
            padding-left: 2rem;
            
            input[type="checkbox"] {
                position: absolute;
                opacity: 0;
                
                & + label::before {
                    content: "";
                    position: absolute;
                    left: 0;
                    top: 0.25rem;
                    width: 1.25rem;
                    height: 1.25rem;
                    border: 2px solid #ccc;
                    border-radius: 4px;
                    transition: all 0.3s ease;
                }
                
                &:checked + label::before {
                    background: #540099;
                    border-color: #540099;
                }
                
                &:checked + label::after {
                    content: "✓";
                    position: absolute;
                    left: 0.25rem;
                    top: 0.25rem;
                    color: white;
                    font-size: 0.875rem;
                }
                
                &:focus + label::before {
                    box-shadow: 0 0 0 3px rgba(84, 0, 153, 0.2);
                }
                
                &:disabled + label {
                    opacity: 0.7;
                    cursor: not-allowed;
                }
            }
        }
    }
}

Task 2: Create an Interactive Menu System

Task

Create a multi-level navigation menu with:

• Hover states
• Active states
• Current page indication
• Mobile responsiveness

Answer

.magical-menu {
    /* Base styles */
    --menu-bg: white;
    --menu-hover: #f5f0ff;
    --menu-active: #540099;
    
    /* Menu container */
    .nav {
        display: flex;
        gap: 1rem;
        
        @media (max-width: 768px) {
            flex-direction: column;
        }
        
        /* Menu items */
        .nav-item {
            position: relative;
            
            /* Link styles */
            > .nav-link {
                display: block;
                padding: 0.5rem 1rem;
                color: #333;
                text-decoration: none;
                transition: all 0.3s ease;
                
                &:hover {
                    background: var(--menu-hover);
                }
                
                &:is(.active, [aria-current="page"]) {
                    color: var(--menu-active);
                    font-weight: 500;
                }
                
                /* Dropdown indicator */
                &:has(+ .dropdown)::after {
                    content: "▼";
                    margin-left: 0.5rem;
                    font-size: 0.75em;
                }
            }
            
            /* Dropdown menu */
            .dropdown {
                position: absolute;
                top: 100%;
                left: 0;
                min-width: 200px;
                background: var(--menu-bg);
                box-shadow: 0 2px 10px rgba(0,0,0,0.1);
                opacity: 0;
                visibility: hidden;
                transform: translateY(10px);
                transition: all 0.3s ease;
                
                @media (max-width: 768px) {
                    position: static;
                    box-shadow: none;
                    transform: none;
                    display: none;
                }
                
                .nav-item {
                    .nav-link {
                        padding: 0.75rem 1rem;
                        
                        &:hover {
                            background: var(--menu-hover);
                        }
                    }
                }
            }
            
            /* Show dropdown on hover */
            &:hover > .dropdown {
                opacity: 1;
                visibility: visible;
                transform: translateY(0);
                
                @media (max-width: 768px) {
                    display: block;
                }
            }
            
            /* Active state */
            &:active > .nav-link {
                transform: translateY(1px);
            }
        }
    }
}

Additional Study Materials 📖

• MDN Pseudo-classes
• CSS Selectors Level 4
• CSS-Tricks Guide to Pseudo-classes

References 📚

1. W3C Selectors Level 4
2. MDN Web Docs - Pseudo-classes
3. CSS Working Group - Selectors

Conclusion 🎉

Remember, young style wizards:

• Pseudo-classes are powerful state managers
• Consider accessibility in your states
• Test all possible state combinations
• Keep selectors specific but not too complex
• Maintain consistent state behavior

Dumbledore's Final Words

"Like a wizard's spell changing based on intention and circumstance, pseudo-classes allow our elements to respond dynamically to user interaction and context. Use them wisely!" 🧙‍