*{
box-sizing:border-box;
}

body{
margin:0;
padding:0;
min-height:100vh;
background:linear-gradient(135deg,#eef2ff,#f8fbff,#eefbf1);
font-family:Arial;
color:#1d2a44;
}

.container{
width:min(980px,94%);
margin:auto;
padding:35px 0 50px;
}

.topbar{
display:flex;
justify-content:space-between;
gap:20px;
align-items:center;
background:white;
border-radius:24px;
padding:26px 30px;
box-shadow:0 18px 45px rgba(31,64,130,.10);
margin-bottom:24px;
}

h1{
margin:0 0 8px;
font-size:34px;
}

.progress{
min-width:120px;
text-align:center;
background:#2451d1;
color:white;
font-weight:bold;
font-size:22px;
padding:17px;
border-radius:18px;
}

.equation-box{
background:#2451d1;
color:white;
font-size:34px;
font-weight:bold;
text-align:center;
padding:28px;
border-radius:24px;
margin-bottom:24px;
}

.example-box,
.step-box,
.finish-card{
background:white;
border-radius:22px;
padding:24px 28px;
margin-bottom:20px;
box-shadow:0 14px 35px rgba(31,64,130,.10);
border:2px solid rgba(198,213,245,.75);
}

.step-box.locked{
opacity:.45;
}

.answer-row{
display:flex;
gap:12px;
align-items:center;
}

input{
flex:1;
padding:14px 16px;
font-size:20px;
border-radius:14px;
border:2px solid #b8c8ea;
}

button{
padding:14px 20px;
font-size:18px;
border:none;
border-radius:14px;
background:#2451d1;
color:white;
cursor:pointer;
font-weight:bold;
}

button:disabled{
background:#9caad0;
cursor:not-allowed;
}

button.secondary{
background:#eef3fb;
color:#2451d1;
}

.message.good{
color:#17803b;
font-weight:bold;
}

.message.bad{
color:#d13232;
font-weight:bold;
}

.finish-card{
text-align:center;
padding:54px 30px;
}

.mini-vzor{
background:#111827;
color:white;
padding:12px;
border-radius:10px;
margin-bottom:10px;
font-family:monospace;
text-align:center;
}

.step-hint{
background:#f3f4f6;
border-left:4px solid #3b82f6;
padding:10px 14px;
border-radius:10px;
margin-bottom:12px;
}

.footer-buttons{
display:flex;
justify-content:center;
gap:14px;
margin-top:26px;
}

@media(max-width:700px){

.topbar{
flex-direction:column;
align-items:flex-start;
}

.answer-row{
flex-direction:column;
}

button{
width:100%;
}

.equation-box{
font-size:25px;
}
}