```
<think>
Let me reflect on the CSS styling and component issues we encountered and formulate a set of best practices for working with Vue components and CSS. This will help avoid similar issues in the future.

Key issues we encountered:
1. CSS variable syntax: Using parentheses `(--variable)` instead of the correct `var(--variable)` or `[--variable]` in Tailwind
2. Class inheritance in Vue components: Vue doesn't automatically apply parent component classes to child components
3. Component styling vs. functionality separation: Mixing component logic with styling created confusion
4. Debugging complexity: Difficulty in tracing why styles weren't being applied
5. Default vs. override styles: Challenges in determining which styles take precedence

I'll formulate a comprehensive set of best practices focusing on:
- Vue component styling patterns
- CSS variable usage in Vue and Tailwind
- Debugging styling issues
- Separation of concerns
- Component design principles
</think>
```

# Best Practices for Vue Component Styling: Lessons Learned

Based on our experience with the `PromptInput` styling issue, here are some best practices to follow when working with Vue components and CSS, particularly in applications using Tailwind CSS:

## 1. Component Styling Patterns

**Rule: Use Wrapper Elements for Component Styling**
```vue
<!-- Recommended ✅ -->
<div class="my-custom-styles">
  <MyComponent>
    <!-- Content -->
  </MyComponent>
</div>

<!-- Avoid ❌ -->
<MyComponent class="my-custom-styles">
  <!-- Content -->
</MyComponent>
```

**Why**: Vue's class inheritance system can be unpredictable. Wrapper elements give you direct control over styling without relying on Vue's attribute inheritance.

## 2. CSS Variable Usage

**Rule: Use Correct Syntax for CSS Variables**
```css
/* In Tailwind classes */
/* Correct ✅ */
class="max-w-[var(--my-variable)]"
/* or */
class="max-w-[--my-variable]"

/* Incorrect ❌ */
class="max-w-(--my-variable)"
```

**Why**: Tailwind arbitrary values require square brackets, not parentheses. When using `var()` syntax, it must be inside the square brackets.

## 3. Component Design

**Rule: Separate Styling from Component Logic**
```vue
<!-- Component (PromptInput.vue) -->
<template>
  <div>
    <slot></slot>
  </div>
</template>

<!-- Usage -->
<template>
  <div class="styling-container">
    <PromptInput />
  </div>
</template>
```

**Why**: Components should focus on functionality and structure, while styling should be applied at the implementation level. This improves reusability and maintainability.

## 4. CSS Variable Definition

**Rule: Define CSS Variables at the Appropriate Scope**
```css
/* Global variables in a main CSS file */
:root {
  --primary-color: #3498db;
  --breakpoint-md: 768px;
}

/* Component-specific variables */
.component-container {
  --component-spacing: 1rem;
}
```

**Why**: Properly scoped variables prevent conflicts and make it clear where values are defined.

## 5. Debugging Styling Issues

**Rule: Use Temporary Visual Debugging Techniques**
```vue
<!-- Add temporary debug visualization -->
<pre v-if="debug" class="debug-info">
  Props: {{ JSON.stringify(props) }}
  Classes: {{ JSON.stringify($attrs.class) }}
</pre>
```

**Why**: Visualizing component props and attributes helps identify why styles aren't being applied as expected.

## 6. Class Overrides

**Rule: Use the `!important` Flag Sparingly and Deliberately**
```html
<!-- When necessary to override base styles -->
<div class="base-styles !rounded-lg !p-4">
  <!-- Content -->
</div>
```

**Why**: Using `!important` (via Tailwind's `!` prefix) should be a deliberate choice, not a default approach to styling problems.

## 7. Component API Design

**Rule: Keep Component Props Focused on Behavior, Not Styling**
```js
// Good ✅
defineProps({
  isLoading: Boolean,
  maxHeight: [Number, String]
})

// Avoid for styling ❌
defineProps({
  className: String,
  color: String,
  rounded: Boolean
})
```

**Why**: Components with many style-related props become harder to maintain. Style customization is better handled via CSS classes at the implementation level.

---

By following these practices, you'll create more maintainable, predictable, and reusable components while avoiding the common pitfalls we encountered with the `PromptInput` component styling.