body {
  margin: 0;
  background: #f6f8fb;
  font-family: 'Inter', 'Segoe UI', Arial, sans-serif;
  color: #232b3a;
  min-height: 100vh;
}
.sticky-header {
  background: #263448;
  box-shadow: 0 2px 10px #0001;
  position: relative;
  z-index: 10;
  padding-bottom: 0;
}
.header-content {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 32px;
  padding: 0 22px;
}
.site-brand {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 18px 0 8px 0;
  flex-shrink: 0;
}
.site-brand img {
  height: 46px;
  width: 46px;
  border-radius: 9px;
  background: #fff;
  box-shadow: 0 1px 8px #0001;
  object-fit: contain;
}
.site-brand span {
  font-size: 2rem;
  font-weight: 700;
  color: #fff;
  letter-spacing: -1.5px;
  text-shadow: 0 2px 12px #0001;
  display: inline-block;
}
.site-tagline {
  color: #48e2ae;
  font-size: 1.08em;
  font-weight: 500;
  margin-left: 6px;
  margin-bottom: 4px;
}
nav.navbar {
  margin-left: auto;
  display: flex;
  gap: 24px;
}
nav.navbar a {
  color: #fff;
  text-decoration: none;
  font-size: 1.13em;
  font-weight: 500;
  padding: 8px 0;
  transition: color .16s;
  position: relative;
}
nav.navbar a:hover,
nav.navbar a:focus {
  color: #5fe0ba;
}
.center-wrapper {
  min-height: calc(100vh - 150px);
  display: flex;
  align-items: center;
  justify-content: center;
}
.main-container {
  max-width: 540px;
  margin: 0 auto;
  padding: 36px 22px 32px 22px;
  background: #fff;
  border-radius: 18px;
  box-shadow: 0 2px 32px #a1b4c726;
  text-align: center;
}
.main-container h1, .main-container h2 {
  margin-top: 0;
  font-weight: 700;
  color: #25314c;
}
.main-container h2 {
  font-size: 1.44em;
  margin-bottom: 26px;
}
.main-container h3 {
  font-size: 1.13em;
  font-weight: 600;
  margin-top: 2.3em;
  margin-bottom: 0.8em;
}
.main-container ul, .main-container ol {
  text-align: left;
  padding-left: 1.25em;
  margin: 18px 0;
}
.main-container li {
  margin-bottom: 8px;
}
form input[type="file"] {
  font-size: 1em;
  margin-top: 14px;
  margin-bottom: 20px;
}
form button,
#convertBtn,
button,
input[type=submit] {
  display: inline-block;
  margin: 0 auto;
  padding: 14px 44px;
  border: none;
  background: linear-gradient(90deg, #24e0a0 50%, #1aa4ec 100%);
  color: #fff;
  border-radius: 9px;
  font-size: 1.23em;
  font-weight: 700;
  cursor: pointer;
  box-shadow: 0 2px 10px #b5e5fa25;
  transition: background 0.19s, box-shadow 0.19s;
}
form button:hover,
#convertBtn:hover,
button:hover,
input[type=submit]:hover {
  background: linear-gradient(90deg, #1aa4ec 10%, #24e0a0 100%);
  box-shadow: 0 4px 16px #1aa4ec21;
}
.alert {
  margin: 22px auto 18px auto;
  padding: 18px 22px;
  border-radius: 10px;
  font-size: 1.08em;
  line-height: 1.7;
  box-shadow: 0 2px 10px #0001;
  max-width: 96%;
  text-align: center;
}
.alert.success { background: #e7fbe9; color: #188a51; border: 1px solid #b3f5cc;}
.alert.error   { background: #fff3f3; color: #d33; border: 1px solid #fcc;}
.alert.warn    { background: #fffbe8; color: #ad7100; border: 1px solid #fbeea0;}
.result-center {
  text-align: center;
  margin: 18px 0;
}
.loader-spin {
  border: 4px solid #eaf4fb;
  border-top: 4px solid #19c589;
  border-radius: 50%;
  width: 44px;
  height: 44px;
  animation: spin 1s linear infinite;
  margin: 0 auto 14px auto;
}
@keyframes spin { 0%{transform:rotate(0deg);} 100%{transform:rotate(360deg);} }
footer {
  font-size: 1.02em;
  color: #b3f7e1;
  background: #263448;
  text-align: center;
  margin-top: 64px;
  padding: 22px 0 13px 0;
  border-top-left-radius: 18px;
  border-top-right-radius: 18px;
  box-shadow: 0 -2px 8px #0001;
}
footer a { color: #7fe0bf; text-decoration: none; margin: 0 7px;}
footer a:hover { text-decoration: underline; color: #fff;}
@media (max-width: 800px) {
  .header-content { flex-direction: column; gap: 2px; align-items: flex-start;}
  .site-brand img { height: 38px; width: 38px;}
  nav.navbar { margin-left: 0; margin-top: 8px; flex-wrap: wrap; gap: 11px;}
  .sticky-header, .site-tagline, nav.navbar { padding-left: 8px; padding-right: 8px;}
  .main-container { max-width: 99vw; margin: 20px 5px 0 5px; padding: 20px 7px 22px 7px;}
}
.center-wrapper {
  min-height: calc(100vh - 150px);
  display: flex;
  align-items: center;
  justify-content: center;
}