/* 全局与主题 */
:root{
  --bg: #f5fbfb;
  --card: #ffffff;
  --text: #0b2b33;
  --muted: #56727a;
  --primary: #17a2b8;   /* 蓝绿 */
  --primary-dark: #108a9c;
  --accent: #2dd4bf;    /* 绿松 */
  --danger: #e74c3c;
  --ring: rgba(23,162,184,0.35);
  --shadow: 0 10px 25px rgba(0,0,0,0.08);
}

html,body{
  height:100%;
  margin:0;
  font-family: "Microsoft YaHei", "Segoe UI", Roboto, Helvetica, Arial, "PingFang SC", "Hiragino Sans GB", "Heiti SC", "WenQuanYi Micro Hei", sans-serif;
  background: var(--bg);
  color: var(--text);
}

.container{
  min-height:100%;
  display:flex;
  align-items:center;
  justify-content:center;
  padding: 24px;
}

.card{
  background: var(--card);
  border-radius: 16px;
  box-shadow: var(--shadow);
  padding: 28px 24px;
  width: 100%;
  max-width: 420px;
}

.brand-accent{
  width: 84px;
  height: 6px;
  background: linear-gradient(90deg, var(--primary) 0%, var(--accent) 100%);
  border-radius: 999px;
  margin-bottom: 18px;
}

.form{
  display:flex;
  flex-direction:column;
  gap: 12px;
}

.label{
  font-size: 14px;
  color: var(--muted);
}

.input{
  padding: 12px 14px;
  border: 1px solid #e3eef0;
  border-radius: 12px;
  font-size: 16px;
  outline: none;
  background: #fbfeff;
  transition: box-shadow .2s, border-color .2s, background .2s;
}
.input:focus{
  border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--ring);
  background: #fff;
}

.btn{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  padding: 12px 16px;
  border: none;
  border-radius: 12px;
  font-size: 16px;
  cursor: pointer;
  transition: transform .05s ease, background .2s;
}
.btn:active{
  transform: translateY(1px);
}
.btn.primary{
  background: linear-gradient(135deg, var(--primary) 0%, var(--accent) 100%);
  color: #fff;
}
.btn.primary:hover{
  filter: brightness(0.98);
}
.btn.secondary{
  background:#eef7f8;
  color: var(--text);
}

.error{
  min-height: 22px;
  margin: 6px 0 0;
  color: var(--danger);
  font-size: 14px;
}

.hint{
  margin: 14px 2px 2px;
  color: var(--muted);
  font-size: 13px;
}

.visually-hidden{
  position:absolute;
  width:1px;
  height:1px;
  margin:-1px;
  border:0;
  padding:0;
  white-space:nowrap;
  clip-path:inset(100%);
  clip:rect(0 0 0 0);
  overflow:hidden;
}

/* 计算器 */
.calc{
  display:grid;
  gap:12px;
  width:100%;
  max-width: 420px;
}
.display{
  background:#ffffff;
  border:1px solid #e3eef0;
  border-radius: 12px;
  padding: 16px;
  font-size: 20px;
  min-height: 56px;
  display:flex;
  align-items:center;
  justify-content:flex-end;
  overflow-x:auto;
}
.keys{
  display:grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}
.key{
  padding: 16px;
  background:#f2fbfc;
  border:1px solid #e3eef0;
  border-radius:12px;
  font-size:18px;
  cursor:pointer;
  transition: background .15s, transform .05s;
}
.key.op{
  background: #e9faf7;
}
.key.equals{
  background: linear-gradient(135deg, var(--primary) 0%, var(--accent) 100%);
  color:#fff;
  border:none;
}
.key:active{
  transform: translateY(1px);
}
.key:focus{
  outline:none;
  box-shadow: 0 0 0 4px var(--ring);
}

@media (max-width: 420px){
  .card{ padding: 22px 18px; }
  .key{ padding: 14px; font-size: 17px; }
  .display{ font-size: 18px; }
}