Responsive form page — centered card, mobile-friendly

A complete login/register page: centered card, responsive, branded. The pattern every auth page uses.

style.css v3.1

style.css — the CSS rules

body {
  margin: 0;
  font-family: -apple-system, system-ui, sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
}

.auth-card {
  background: white;
  border-radius: 16px;
  padding: 2.5rem;
  width: 100%;
  max-width: 400px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}

.auth-card .logo {
  text-align: center;
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.auth-card h1 {
  text-align: center;
  font-size: 1.4rem;
  margin: 0 0 0.3rem 0;
  color: #1a1a1a;
}

.auth-card .subtitle {
  text-align: center;
  color: #666;
  font-size: 0.9rem;
  margin-bottom: 2rem;
}

.form-group {
  margin-bottom: 1.2rem;
}

.form-group label {
  display: block;
  font-size: 0.85rem;
  font-weight: 600;
  color: #333;
  margin-bottom: 0.4rem;
}

.form-group input {
  width: 100%;
  padding: 0.7rem 0.9rem;
  border: 2px solid #ddd;
  border-radius: 8px;
  font-size: 0.95rem;
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
  box-sizing: border-box;
}

.form-group input:focus {
  border-color: #667eea;
  box-shadow: 0 0 0 3px rgba(102,126,234,0.2);
}

.btn-submit {
  width: 100%;
  background: #667eea;
  color: white;
  border: none;
  padding: 0.8rem;
  border-radius: 8px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  margin-top: 0.5rem;
  transition: background 0.15s;
}

.btn-submit:hover {
  background: #5568d3;
}

.auth-card .footer-link {
  text-align: center;
  margin-top: 1.5rem;
  font-size: 0.88rem;
  color: #666;
}

.auth-card .footer-link a {
  color: #667eea;
  text-decoration: none;
  font-weight: 600;
}

index.html — the HTML structure (what the CSS targets)

<div class="auth-card">
  <div class="logo">&#9889;</div>
  <h1>Welcome back</h1>
  <p class="subtitle">Log in to your account</p>
  <form>
    <div class="form-group">
      <label>Email</label>
      <input type="email" placeholder="you@example.com" required>
    </div>
    <div class="form-group">
      <label>Password</label>
      <input type="password" placeholder="••••••••" required>
    </div>
    <button type="submit" class="btn-submit">Log In</button>
  </form>
  <div class="footer-link">
    Don't have an account? <a href="#">Sign up</a>
  </div>
</div>

Live preview updates as you type

🧠 How it works

body is a flex container, centered — the card is always in the middle of the screen. background: linear-gradient — a nice purple gradient. Change it to match your brand. min-height: 100vh + padding: 1rem — fills the viewport, with a small margin on mobile. max-width: 400px + width: 100% — responsive: 400px on desktop, full width (minus padding) on mobile. box-shadow: 0 20px 60px — a big soft shadow makes the card 'float' above the gradient. border-radius: 16px — generous rounding, feels modern. Focus ring color matches the gradient (#667eea) — consistent branding. width: 100% on the button — full-width button, common in auth forms. box-sizing: border-box on inputs — critical! Without it, padding makes inputs wider than 100%.

✏️ Try these changes

Change the gradient from #667eea #764ba2 to #a0c000 #58a6ff
→ green-to-blue gradient
Change max-width: 400px to 350px
→ narrower card
Change border-radius: 16px to 8px
→ less rounded — more 'corporate'
Change the focus color from #667eea to #a0c000
→ focus ring becomes green
Change box-shadow: 0 20px 60px to 0 4px 12px
→ smaller shadow — card feels flatter

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