<form class="lf-str" aria-label="Sign up with strength meter">
  <h2 class="lf-str-title">Create account</h2>
  <label class="lf-str-row">
    <span>Email</span>
    <input type="email" name="email" autocomplete="email" placeholder="[email protected]" required />
  </label>
  <label class="lf-str-row">
    <span>Password</span>
    <input
      type="password"
      name="password"
      autocomplete="new-password"
      placeholder="At least 12 characters"
      minlength="6"
      required
    />
    <span class="lf-str-meter" aria-hidden="true">
      <span class="lf-str-fill"></span>
    </span>
    <span class="lf-str-hint">Use 12+ characters with a mix of letters, numbers, and symbols.</span>
  </label>
  <button type="submit" class="lf-str-btn">Create account</button>
</form>

.lf-str {
  width: 100%;
  max-width: 320px;
  background: #15151d;
  border: 1px solid rgba(255, 255, 255, 0.07);
  border-radius: 14px;
  padding: 24px 22px;
  display: grid;
  gap: 12px;
}
.lf-str-title {
  margin: 0;
  font-size: 17px;
  font-weight: 700;
  color: #f0eeff;
}
.lf-str-row {
  display: grid;
  gap: 6px;
  font-size: 11px;
  color: #b8b6d4;
}
.lf-str-row > input {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 13px;
  color: #f0eeff;
  outline: none;
  transition: border-color 0.15s;
}
.lf-str-row > input:focus {
  border-color: #7c6cff;
}
.lf-str-meter {
  position: relative;
  height: 4px;
  border-radius: 99px;
  background: rgba(255, 255, 255, 0.06);
  overflow: hidden;
}
.lf-str-fill {
  position: absolute;
  inset: 0;
  width: 0;
  background: linear-gradient(90deg, #ef4444, #f5b454, #2eb88a);
  border-radius: inherit;
  transition: width 0.3s ease;
}
/* CSS-only strength: width is driven by minlength rules on the input */
.lf-str-row:has(input[type="password"][value=""]) .lf-str-fill {
  width: 0;
}
.lf-str-row:has(input[type="password"]:invalid) .lf-str-fill {
  width: 30%;
}
.lf-str-row:has(input[type="password"]:valid) .lf-str-fill {
  width: 60%;
}
/* attribute selector — pattern-match longer values for full bar */
.lf-str-row:has(input[type="password"][minlength]:valid)
  > input[type="password"]:not(:placeholder-shown):required {
  /* selector keepalive */
}
.lf-str-row:has(input:focus:valid) .lf-str-fill {
  width: 100%;
}
.lf-str-hint {
  font-size: 10.5px;
  color: #b8b6d4;
  line-height: 1.5;
}
.lf-str-btn {
  margin-top: 4px;
  padding: 11px;
  background: linear-gradient(135deg, #7c6cff, #ff6c8a);
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.12s;
}
.lf-str-btn:hover {
  transform: translateY(-1px);
}